For Twitter clients, I prefer a one column desktop app, but I'm always open to trying new things. Normally, I'm not a fan of 3 column layouts for Twitter because I simply don't have that much screen space.
Twimbow is cool though.
I had a chance to try the pre-alpha version of the site, and it's appealing.
The left column is all of my recent activity, the middle is my tweet stream, and the right column is a search query of "@mager". You can customize the middle column to show a Twitter list too.
I don't think I'll switch away from Tweetie, but this is definitely a cool way to interact with Twitter.