Its design is brilliant—I am similarly a fan, though I don't Twitter—but my point was that "killer app" means something that "the best twitter client I've ever used" does not.

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.

Communication isn't a human invention.

Twitter is a human invention. Written communication (arguably) is a human invention.

Audio from the talk will be available on http://2009.dconstruct.org/podcast/ soon.

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.

Filtering information is not a new idea at all.