GM, Odeon still runs on WB 3.5. I tried it out today. Still looks ok, just doesn't skin some parts (the parts that WB4 skins).
This was not a slight against WB4. I think it's a great application. When all the testing is finished I'll download it again through ODN and run it from that point on, it's just, right now, while it's still an alpha, it causes some problems with the GUI on my system. Occasionally, parts of the GUI won't skin properly and those parts become unreadable. Since my wife uses this computer for work, I can't keep WB4 on it right now. It's just a temporary thing.
I've actually been updating a number of my skins to the WB4 format. Skins like 'Mood Indigo', 'Celeb', and 'Spander' have all been updated. I'm just waiting for the final finished release of WB4 before I upload the updates to WC.