Well, last I heard was that the UB code was taken over by another company in the spirit of continue developing it. Current and latest release is version 2.21a (official) but there is also a 2.22 version available. It has been sais that version 3 should be released in the end december (earliest) or beginning of next year and then it will also be a php based script. Clostest site for more info and keep up the dialog would currently be:
http://www.ultraboard2x.net/
I have thought about moving my installtion of forum from UB couple of times but never really found anything a liked. Closest script that I really enjoy to work with is phpBB. There are couple of features that I like better but I have to say that I still find UB much better than the most script I compared it with. And it still does the jobb good enough.
/Kim