Shu is part of a growing group of consumers who look to their smartphones — Internet-enabled mobile phones — to save money and stay informed when buying. Nearly six in 10 mobile users say they’ll be using their phones for holiday shopping, and retailers are falling all over themselves to offer applications and mobile websites to meet the demand. With smartphones, shoppers can compare prices, store loyalty and gift cards, make wish lists and get discounts at their favorite stores.

But retailers also risk alienating customers if the apps and mobile websites fail to deliver. More than half of customers surveyed say they won’t return to a mobile site if they’ve had a poor experience, according to a study by Gomez, Compuware‘s unit that studies website performance.

And performance expectations are high: Nearly 60% of people anticipate mobile sites will run as smoothly as or better than sites they visit on their computers, the Gomez study showed. Meeting the challenge has been difficult. Consumers ranked the performance of mobile sites of the Thanksgiving holiday weekend’s 15 largest retailers as “tolerable,” compared with the retail websites overall.

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Much of the interest in mobile has occurred in the past year — 25% of consumers say they’ll be turning to their phones more than they did in 2009, according to a study by the Mobile Marketing Association and Luth Research. And the mobile apps centered on shopping aren’t just for fun and flash. They could mean real savings for consumers, especially those who search for better prices. Scouting locations where gifts are sold and comparing prices ranked as the top two reasons consumers plan to use their phones during holiday shopping.

Mobile phones offer shoppers the resources of the Web while they’re in a store and enable retailers to deliver the most relevant deals. But shoppers can also use them to make purchases with their credit or debit cards, though they could be opening themselves up to identity theft, says John Hering, CEO and co-founder of Lookout Mobile Security. “The mobile device has become the most personal computer and, with that, identity thieves are now beginning to turn their sights to smartphones,” he says.

Retailers have long matched rivals’ prices, and shoppers search ads in fliers or on the Internet to find the best offers. Now, consumers can discover competitors’ prices while in a store, thanks to mobile sites and apps such as PriceGrabber, which more than half a million consumers have downloaded.

The iPhone and Android application is the mobile incarnation of PriceGrabber’s website, which attracts about 26 million shoppers each month. Using the mobile app, shoppers can scan an item at a store and see information on the best price on the product across multiple retailers. They can try to haggle for a better deal while they’re in the store, or buy it for less through a competitor PriceGrabber has discovered. The service even calculates exactly how much the purchase will be when shipped directly to a consumer’s home, showing which option is the least expensive down to the last cent, PriceGrabber President Laura Conrad says.

“The difference in prices is pretty significant for most of the sellers we have up there,” says Conrad. “On any given day, most of these sellers could be running a special. Online retailers can change them on the fly.”

On Black Friday, consumers used the iPhone app most often to search for price comparisons on electronics, computers, cameras, appliances and toys, the company reported.

LaKeitha Luster, 36, of Natchez, Miss., says she’s always compared prices before big purchases, but now she’s pulling out her smartphone to do the task. Getting comprehensive product information through the mobile sites can prove challenging, though, she says. “When you look at items online (particularly on a BlackBerry), I don’t normally get a full description of what I’m interested in purchasing,” Luster says.

Shopping-focused apps could help customers earn rewards and cut back on unnecessary travel expenses to get to a store. The iPhone and Android app CheckPoints earns shoppers points when they take pictures of the bar codes of items the app chooses to feature. The points are redeemable for gift certificates from retailers such as Sephora and Neiman Marcus, plus gadgets, airline miles and charity donations. Another app, Shopkick, enters people in sweepstakes just for doing what’s known as “checking in” — alerting the app that they’ve walked into a particular store.

Social-networking giant Facebook has gotten involved in mobile check-ins with its Facebook Places service. Shoppers could get deals for checking in once, returning to a store or bringing friends to a store. Gap, Macy‘s and American Eagle Outfitters are among those offering discounts this way.

Some mobile apps deliver deals based on a customer’s preferences and where they are, thanks to location-finding technology that tracks where a customer shops and what items they check out. Mobile app developer Yowza claims it has saved users more than $5.4 million.

The app hunts down coupons from nearby retailers and sends vouchers straight to shoppers’ phones, which cashiers can scan at checkout. Lane Bryant, which has offered “buy one, get one free” deals through the app, is among the more than 300 brands Yowza has enlisted.

Mobile devices can also combine tasks that consumers have typically done only in stores or only from their computers. “Stores are really starting to understand that the lines between online and brick-and-mortar stores are blurring right now,” Conrad says, pointing to retailers such as Walmart that have added Wi-Fi service so customers can go online while shopping in a store.

Mobile smartphones also deliver online information to shoppers at traditional malls. Many big malls and department stores are hopping on board:

•Mall operator Simon Property Group offers an iPhone app that can automatically notify a shopper’s social network when she has checked into a particular store at the mall. The Simon app also delivers specialized deal alerts and can help shoppers remember where they parked.

•General Growth Properties gives consumers access to promotions and discounts at its 150-plus malls nationwide through its Club Shopping Mall Guide app. GPS-based store directories help shoppers navigate the malls. Shoppers also can play mobile games for prizes. For instance, the app might display a picture of a snow globe, prompting consumers to shake their phones for the chance to win a $100 mall gift card or to enter a sweepstakes for a $500 gift card, depending on what the virtual snow globe reveals.

•J.C. Penney has built a mobile-compatible website and an app for the iPhone and Android phones. Both provide a peek at weekly sales circulars and help in finding the nearest store. It also lets shoppers create mobile wish lists, take advantage of coupons and access their store rewards account.

•Target‘s mobile website and apps store prices to help customers compare deals. The chain also offers coupons that can be scanned and redeemed from the smartphone.

“It can detect when a consumer comes in a store and offer specialized incentives right on the spot,” says Bob Egner, vice president of global marketing at EPiServer, a software company that powers e-commerce websites.

Consumers could also better prepare themselves for big holiday shopping trips by using apps that make store loyalty cards virtual, as Shu did.

Mobile app Swagg’s aim is for users to “have everything, carry nothing” — in their wallets, that is, says Rocco Fabiano, president of Firethorn Holdings, Qualcomm‘s mobile commerce subsidiary. The mobile tool stores up to 300 loyalty and gift cards on a smartphone.

Swagg also delivers deals straight to the mobile screen, much like Yowza. There are more than $55,000 in discounts from more than 3,000 brands available through the app, Fabiano says. Users can choose which types of offers they’d like to see.

Shoppers could even cut shipping costs on gifts and send last-minute presents through mobile-gifting services. Swagg has at least half a dozen retailers on board for its gift card swap service, where people can send a gift card right to a loved one’s smartphone. The app is working on getting more retailers to participate in this service. Options now might be a bit limited.

Mobile apps may also help shoppers better filter discounts and inventory on big e-commerce sites. The eBay Deals app for iPhone brings users daily deals and enables customized searches for bargains.

The Overstock.com mobile app has all the same shopping and search capabilities as the website and could also help shoppers ring in extra savings through its Lott-O function, which offers exclusive chances to win extra savings.

Some shoppers might be wary of closing transactions on their smartphone, though, and may opt to browse for deals on their phones but pay from their computers, says Sandeep Bhanote, CEO of mobile retail software provider Global Bay Mobile Technologies.

Egner says brands need to pay attention to the palm-size screen. “If you want to be a retailer, you’ve got to have a mobile site to be competitive,” he says.

Shu is skeptical of the security of the information on his smartphone, but he’s still loading it with reward cards, tracking down coupons and scanning bar codes.

His phone, he says, is “a very convenient tool” that helps him decide “how and where we shop.”