I started using bDule today after reading about it on Techcrunch. It seems to be very nearly the perfect twitter client for me - decent multi-account support, Facebook integration and reasonably snappy. Also, and this is really important for me, it's not oppressively black.
The group feature isn't quite there yet, it doesn't list all my friends and there's no way to edit a group after you create it. There's also no spell checker and getting the right layout is unnecessarily awkward. It's still in alpha so there's good reason to hope that these problems will be addressed soon.
I wonder where the name comes from. It makes me think of a certain casual game where you swap gemstones around until you're ready to chew your eyeballs out. I'm the last person to talk about puzzling software names though.
bDule is WPF/.NET3.5 so only runs on Windows XP or better. It also seems to suffer from the same creeping memory usage that plagues other desktop Twitter clients. I really wish someone would start offloading the stream into a database. I've got nearly frustrated enough with this to write my own Twitter client a couple of times, but it's not exactly an uncrowded market.
If you're a Windows tweeter give bDule a try.