Well, I have a Ubiquio 501 and I must say there were originally some problems with crashing, especially on the old ROM. Fortunately, Expansys is very proactive about it, and they have released a new ROM so you can flash the phone yourself. The new ROM is incredibly stable and now the phone is rock solid.
The good news is that an even newer ROM release is going to be available soon!
Is it running the AKU 3.3? (if it is you should get a screen during boot up saying Microsoft Direct Push
Do the keys make a loud click when typing? minor thing I know but I think that would put me off the thing.