IE9 is still in BETA and is still far too buggy - it has issues with vB and a few other everyday websites and standards. It does seem as though the BETA is a very early release to make people aware of the forthcoming release and probably should have been kept behind closed doors in all honesty, as it feels somewhat similar to an Alpha build when in general usage.
IE9 has some smashing new features, but until they finish it, it is IE8 or Opera for me im afraid. It's all well and good these wonderful new features, but theres no point in trying to run before you can walk Uncle Steve.
On a more positive note, UBB and more importantly, Wiki, appears to be fully compliant and working 100%...