I have recently joined twitter, mostly because of the hype and not because I see any very good use
All people complain about the stability and I can really understand why. Since I am not using any twitter client currently and their IM Jabber service is still down, I have to use the website. It sometimes loads slow or not at all which is really annoying. I can understand why power users hate that.
What I noticed when searching users from Stuttgart is that users which you already follow are displayed in a different color and have some options aside. So, for every search you do, the database table with the people you follow is checked too. This is of course very nice for usability but if everything in twitter is luxurious like that then no wonder they have issues about their load.
By the way, Sebastian is also on twitter.