To many tweets!
Twitter has really taken off in that pass 6 months. People are signing up like crazy and new tools are popping up like crazy. People are following thousands of others and are trying to find the best way to manage all those tweets. TweetDeck has become one of the leaders as a desktop tool to view all the tweets you are following. The abbility to split the tweets up in to different groups / columns makes it far easier to organize the tweets you really want to read.