Opera 10 works for me
As an Opera user for several years (from before Firefox appeared), I can say I think this is a good upgrade... it works faster than 9.64, no stability (or other) problems so far.
I prefer Opera to Firefox mainly because I think there are more user options that suit my preferences (toolbars, options etc.) ... and old habits "die hard"
I am on XP pro on a fairly new box... the fact my daughter's Vista Laptop was using over 1G of memory before starting to do anything persuaded me to stick with XP !!!
Regards
Martin