Twitter has a "lists" feature, where you can group Twitter handles and then check in on subsets of Twitter users, instead of your whole Twitter list. I primarily use the feature for my "friends" list of people I want to watch more closely. I typically check that list to see what those folks are doing, and then just scan everything else. (I also subscribe to some searches that I monitor from time to time.) Other lists I have cover groups that I happen to be in: KM, TOC, Boston, and several others. An interesting pair is "people I've met" and "people to meet." The first is obvious - people I've met in the flesh. And the second isn't comprehensive, but rather people that I've decided would be interesting to meet for some reason or another.
Twitter also tells you about the lists that other members have selected for you. Based on a blog entry from Harold Jarche last month, I had a look at the lists that I am in, and created the Wordle cloud below. Correction: about 1/3 of the 100+ lists I am on are "knowledge management," so I have removed that entry from the list as it completely swamps out everything else.
Beyond the huge KM emphasis, it's interesting to see the other groupings people used for me. It also gives me a hint about job hunting and where I should focus my efforts.