They walk the Las Vegas Strip in groups of as few as four or five or as many as two dozen -- men or women only, most of them in matching attire or other apparel signifying their unity. Often, their evening is devoted to a relentless pursuit of alcohol consumption.

We're talking, of course, about bachelors and bachelorettes.

"We don't have any hard data on what the number of people would be specifically coming for bachelor or bachelorette parties, but obviously that is a huge, huge number," said Erika Pope, spokeswoman for the Las Vegas Convention and Visitors Authority. "Tour companies have evolved to meet this niche, and that certainly underscores how it's become its own viable thing."

Of Vegas' 39.2 million visitors in 2007, 49 percent stated leisure or pleasure vacationing as their No. 1 reason, versus 11 percent coming primarily to gamble and 11 percent to visit relatives.

"Of course, of those visitors, the actual percentage who did gamble was 87 percent," Pope said. "It just wasn't the main reason they said they came."

And the gatherings of men or women aren't just for bachelor or bachelorette parties, Pope added.

"College friends, multigenerational trips, women or men who work together -- these are all groups who have been coming to Vegas in larger numbers," Pope said. "That's a trend in the travel industry in general. And sometimes it's that they have their first experience with this particular group at their bachelor or bachelorette party, and then they want to get together with that group on a regular basis, without having to wear that bridal veil around all night."

The real problem for Vegas seems to be where to put them all. The clubs, now celebrity-owned and splitting at their Apple Bottom seams with 20-something hipsters, have two-hour lines at the door. At the peak wedding times -- which is to say now -- the city is a sea of pink boas, tiaras and bands of brothers clutching wads of dollar bills.

"They're always building more clubs and hotel rooms, so I don't think it will ever be so bad that there really isn't room," said David deMontmollin, whose "Las Vegas Little Black Book: A Guy's Guide to the Perfect Vegas Weekend" and "Las Vegas Little Red Book: A Girl's Guide to the Perfect Vegas Getaway" have become go-to guides for folks planning their parties. "I think, though, that the issue is that people start not to feel special because there are so many parties going on they get lost in the shuffle."

As he points out in both books, when you have your party in small-town Iowa, the local Elks Club is going to pull out all the stops, showering you with free drinks and making sure everything goes just right.

"On your big night in Vegas, it's you and hundreds of other bachelorette parties on any given weekend," he said. "You're not going to get any special treatment."