In my previous post (written 5 minutes ago) I talk about Twitter Lists in relation to shared namespaces (Hint: They are not in a shared namespace). Another under-reported fact, however, is that lists are also Tags. They are a great way for Twitter to learn how Twitter users are perceived and grouped (As a side note, they are also great for people to see how other people perceive them - one of my favorite lists in which I am listed: @chadcat/unreasonably-talented haha).
One could easily see an algorithm that can determine accurate APML data about each user not just by looking at their Tweet history, but by also checking their Bios and the Tweet History/Bios of the people they are listed with. The list name itself, in fact, is a very concentrated form of topic/tag data.
Do lists double as Twitter's user tagging feature?
Who will be the first to ship an automated user discovery directory based on analyzing the relationship between users who are on the same lists?
I hope MrTweet is already working on this!