I've had a B-52 AT212 for just over a year now. I too was concerned about the build quality, but was convinced by the 5 year warranty--the company seems out to prove itself. I've had no problems at all. Haven't travelled with it much--mostly in the studio.
As far as sound: I'm still not done finding sounds I like from this thing. The clean is great, and the dirty & heavy sounds are endless--I can dial in any variety I can think of. (The contour & bottom controls help there.)
For recording, I really like the "big" sound you get from more volume, less gain. But this thing is so loud its hard to push the tubes in the power section--so I got a Weber attenuator from Eurotubes. Cranking the amp way up then bringing the volume back down with the attenuator makes for a killer sound.
I also updgraded the tubes with a set from Eurotubes while I was there--that was worth it to me as well.