Tweetdeck syncs with our desktop experience. For people that need to filter the stream to grok it better (read: eventually everyone), Tweetdeck is better.
This reminds me of something Russell Davies spoke about at dConstruct. To paraphrase, TweetDeck is humans solving problems humans have created for themselves.
Tweetdeck also filters Facebook, and others soon too, I'd bet. Given enough time, it would work with your email / chats / voicemail / smoke signals etc.