With Twitter Lists, any Twitter user can create a list of other users and make the list public or private. You can follow others' lists and see what lists you're on (assuming the feature's live for you) by going to http://twitter.com/[username]/lists/memberships (mine are here).

I wrote on 360i's blog about how Twitter Lists are the "Web's newest popularity contest." The next day, Mashable titled one of its posts, "Twitter Lists: Only You Can Help Mashable Beat Barack Obama :)". This is bound to happen, but Lists are easily gamed. Say you're a large company, or a smaller but tech-savvy one, with 100 people on Twitter, and these employees all add your main corporate account to 10 different lists. You're instantly on 1,000 Twitter Lists, which for now will probably put you well in the top 1% of the most popular listed brands on Twitter. Meanwhile, if I'm on 100 lists through 50 people each adding me to two lists, and you're on 75 lists but added by 75 different people, who's more popular? The allure of gamesmanship over this will be short-lived. I hope.

The utility, however, will be far more appealing. The list creation feature has been around in other Twitter applications like Tweetdeck and Seesmic, but this is the first time lists have been available from Twitter itself. It's one of the biggest reasons I haven't spent much time making lists in other Twitter clients; I figured if and when Twitter built in that functionality, such lists would be more portable. That's what's happening now, as Twitter opened its API, and Seesmic already incorporated the feature.

Any Twitter user should find lists worthwhile. I was showing my wife how to make lists of family members, while my mother-in-law may make a list of businesses near her home in Dallas. Marketers should find even more value. Here are five ways marketers can use lists:

1) Aggregate multiple professional accounts if you have several faces of your business on Twitter. It's a natural for businesses like Comcast, which has a number of customer service representatives on Twitter, or Zappos, which has hundreds of employees tweeting. This can also work well for a company like Walmart that has a section on its site with all of its Twitter handles. A newspaper can bring together all of its reporters, or a packaged goods conglomerate can compile all of its brands in lists. Even if these lists don't bring in millions of new consumers or clients as followers, they may be useful for important constituents such as reporters, investors, or employees.

2) Aggregate passionate consumers. If you run a TV show, make a list of tweeters who love talking about every last plot twist. If you're a travel company, consider making lists of some of the most vocal Twitter users in each city where you have a presence. If you're a product manager for a technology brand, pull together all your die-hard fans. At the very least, you'll make it easier for all of these influencers to find each other to expand the noise in your echo chamber. But packaged right, it could be a way to pull in new fans and show others how much passion there is for your brand beyond those on its payroll.

3) Be a resource. Make lists of the most knowledgeable people in your industry, whether they're colleagues, reporters, consumers, or even competitors. While my lists are a work in progress, I've added many friends and people I respect from other agencies to lists. Mostly this will be convenient for me, but I'm more than happy to make these lists public in case they're useful to others.

4) Monitor what lists you're on and what lists include your competitors and peers. It's a way to gauge anecdotal brand perception. You can also find new people to follow this way.

5) Share lists beyond Twitter. It's going to take a while for lists to catch on beyond early adopters; this highly anticipated feature for die-hard tweeters may just be one more thing to learn for casual users. If you cater to early adopters, though, creating useful lists and sharing them in other channels like your site, email newsletters, or Facebook page should resonate.

I'm convinced Twitter Lists will change Twitter, and entirely for the better. I'm very curious what it will do to follower counts, though. When you create a list, you don't need to follow the people on it, even if you're likely to. I might create a list of brands on Twitter without following them and use it as a reference. Additionally, when you follow someone else's list, that probably includes many people you're not following. To counter that though, you may wind up discovering great people to follow.

I also wonder if people will be more likely to increase the number of Twitter users they follow. Now that you can isolate the handful of people you most want to follow and group them in a list, it's easier to run up the count of people you're following without worrying about the glut.

These effects, if they show up at all, won't be noticeable right away. But when you try Twitter Lists, I'd wager it will immediately impact how you use and think about Twitter. And as the feature appears in other Twitter clients over the coming months, lists will be as much a part of the Twitter lexicon as @-replies and direct messages.