Nike.com sells nearly 200 styles of sneakers for men and women -- which, for some footwear fiends, apparently isn't choice enough. In fact, the convenience of being able to shop online isn't enough.

Enter NikeID.com, the Web site where you can design a one-of-a-kind shoe using dozens of colors and fabrics. Candy-apple low-tops with a lime-green swoosh? Caramel trainers with your initials embroidered on the back? Dream up combinations from the colors offered, click until you've got it right, and custom-made shoes can be delivered to your doorstep in about three weeks -- for only $10 or so more than their non-customized counterparts.

While NikeID's shoes have become must-haves among those with a sneaker fetish, they also herald a larger trend: the "just-have." As in, just you have it.

Nike is not alone in offering customized footwear. The "Just Do It" brand has been selling custom designs since 1999 and has more than doubled the number of custom sales every year since then. But when the company relaunched the NikeID Web site this spring with a vastly expanded product lineup, it was part of a small crowd.

There's Shop.vans.com, which offers 11 ways to modify the company's Old Skools -- not to mention eight ways to design their Slip-ons. Converse, which is owned by Nike, has recently jumped into the fray: The month-old ConverseOne.com allows customers to choose colors and patterns for the iconic Chuck Taylor lace-up basketball shoe, with 14 hues for the tongue alone. Its Jack Purcell shoe will be added to the site next month and the One Star this fall.

There's little question that sneakers are big business: U.S. sales topped $16.55 billion last year, a little less than half of the $38.45 billion spent on all footwear, according to market research firm NPD Group. For many people, every day is casual Friday. There's even the concept of the "sneaker wardrobe": a pair for each day of the week. Said Amanda Freeman, vice president of Youth Intelligence, a New York-based trend analysis firm, "It's easy to justify a sneaker collection."

U.S. sneaker sales rose a modest 4.3 percent in 2004, NPD Group says, and brands are struggling to distinguish themselves in a fiercely competitive market.

Customization may help with that, but it may not help the bottom line. Then again, that may not be the motivation.

"My guess is that they don't care" about turning a quick profit, said Marshal Cohen, chief industry analyst at NPD Group. "This is about connecting with the customer."

"It's more about being innovative, showing that you have an understanding of consumer needs," said Michael Wood, vice president of Teenage Research Unlimited, who thinks the customizable offerings may be "a loss leader."

It's also well-suited to the demographic all manufacturers, retailers and broadcasters hunger for: the young.

"This is a consumer who places a lot of value in being unique," said Wendy D. Farina, principal at Kurt Salmon Associates, a retail consulting firm.

This kind of selling certainly has all the right elements: It takes place on the Internet, where young people have found a second home, and teens and twentysomethings wear a lot of sneakers.

Although the sneaker companies decline to cite figures for online sales, making it hard to gauge them, the custom sites have a third, perhaps crucial, advantage: Customizing brand-name shoes lets shoppers behave in ways that are both creative and conformist, a duality that may particularly appeal to teens.

They're "trying to establish their individuality," said Wood, at the same time they're "trying very hard to fit in."

These sites, then, are tailor-made for the teen who wants to stand out enough so his swoosh catches the eye of the kid at the next locker, but not so much that he avoids branded merchandise altogether.

That's a balancing act that gives Alissa Quart, the author of "Branded: The Buying and Selling of Teenagers," pause. "It's yet another way of promoting false choice," she said. "It does encourage at least a small amount of creative thinking," but, she added, "it's a double-edged thing" -- because young buyers are trying to be unique by buying mass merchandise.

Well, not exactly "mass": "It happens one shoe at a time," said David Schriber, Nike's global concepts director. "Consider that a single style can be customized into several million different versions, before you put your name on it -- there is simply no other way to make it happen."

And at only $10 or $15 more than the standard-issue shoes, chances are there's simply no way for a huge company to make lots of money at this.

Profitable or not, the sneaker sites have one very practical application: They open up a wealth of market research possibilities. Thousands of shoppers logging their preferences on the minutiae of laces, tongues and soles amounts to a free focus group.

Industry watchers speculate that companies may plan to use the data supplied by these style-minded shoppers to help design their regular wares. "It's a great way to insert the consumer into the process of product development," Farina said.

In doing so, she said, retailers have "a much better shot at getting it right" when determining what will sell at the Foot Lockers of the world.

NikeID has also focused on grass-roots advertising, targeting such hip folks as 31-year-old blogger Kyle Gustafson. Two months ago, the Alexandria resident was invited to participate in a design contest sponsored by the company. All 20 participants operated blogs, and though Gustafson did not win, he got free shoes that he wrote about on his site, Informationleafblower.com.

To Gustafson, the notion that the company was co-opting his cool for the price of a pair of Nike Dunks was both obvious and of little import. "Nike knows what they're getting from me," he said, "and I know what I'm getting from them."

It's not all success stories in the custom department, though. Reflect.com, a Procter & Gamble site that sold customized makeup and other beauty products, shuttered its doors last month. And Levi's withdrew its custom-fit Original Spin jeans from stores two years ago.

Despite the negatives, online customization doesn't seem likely to disappear anytime soon. When it comes to predicting which products consumers will soon be able to personalize, many analysts say the sky's the limit.

Shoppers are now accustomed to calling the shots when it comes to cell phone ring tones and iPod playlists. Retailers such as Lands' End and Target offer customizable apparel for baby-boomer bodies, while such indie Web sites as Neighborhoodies.com offer customized apparel to a small but stylish audience. But these sneaker companies' efforts represent a bit of both worlds: cool, customizable gear and the mass market.

"Customization is going to be everywhere," Cohen said. "This is definitely one of those sneak peeks into the future."

Users can design shoes on NikeID.com for about $10 more than their ready-made cousins.