Twitter Lists are officially up and running - although they don't seem to be taking off as quickly as Twitter might have hoped. The concept, as we've blogged about recently, is pretty straightforward - you can now create "lists" of Twitter people, and other Twitter users can choose to simply follow those lists, instead of individually following people on those lists.

The implementation, which went live last week for a small selection of users, is pretty awesome. You're now shown, next to your followers and following count, the number of lists in which you're linked; clicking that number will show you each person who's added you to a list, and information about the list you've been added to.

Some Twitter users are concerned, though, that Twitter lists are going to kill #followfriday, that tradition of listing, every Friday, all of the awesome people who you think your Twitter followers might be interested in discovering and following themselves. FollowFriday has been around for a while, and it's a fairly popular way for Twitter users to discover new Twitter users - after all, it's authoritative, meaning that you trust the authority of the person doing the recommending enough to follow the people on their list.

Now that Twitter has taken the core concept of FollowFriday and turned it into a feature built in to the Twitter architecture itself, does this mean the end of #FollowFriday as we know it?

Probably not. At least, not anytime soon.

See, those Twitter lists are currently only available through the Twitter.com website - the major Twitter clients like Seesmic Desktop and Tweetdeck have yet to implement them - and since most people use third-party clients to access Twitter, they're not seeing any information about Twitter lists, or any options to add users to them. For those third-party client users, Twitter lists simply don't exist - and as long as it stays that way, people are going to continue using #FollowFriday as their primary means of recommending and discovering new Twitter users.

We can't guess how long it'll take for the third-party application developers to implement the lists feature into their clients - we expect to start seeing client updates utilizing the functionality within the next week or so. As more and more users update their clients, they'll find the lists feature to be accessible to them - but will they all necessarily use it? Some people won't even be aware that the feature has been implemented, since they're so used to using Twitter in the way that they do, and don't often notice new features being added. Some people will try it out and not like it. Others, though, will certainly start using Lists with a passion - after all, a user who's great at creating lists would probably be someone people would want to follow, and everyone wants to be followed. So we expect to see some "power listers" starting up in the days and weeks to come.

Still, though, this all most likely won't mean the death of #FollowFriday. There's just too many people doing it, and it's become something of a tradition. It's not certain whether or not new Twitter users will prefer #FollowFriday or Twitter lists, or whether users will treat them as mutually exclusive. One thing we do know, though, is that once the hardcore frontrunners start doing something one way on Twitter, they usually don't change it unless they have to - meaning the #followfriday is probably here to stay.