I KNEW there was an SP2 warning I forgot to pay attention to when bringing my new (Win Multimedia Center Edition - SP2) box up. heh
No... as far as I can tell, I haven't had any SP2-related problems in the couple months I've been running my MOTU 828mkII with WDM/KS drivers under Sonar.
(I recently began experimenting with ASIO drivers under Sonar and Tracktion. Yesterday, I had some glitching with the ASIO driver while I was working and switchted to the WDM/KS driver with no further problem. But I didn't pursue/diagnose the problem with the ASIO drivers, yet. I suspect it can be ironed out, but I do not tolerate any glitching, clicks, etc, and didn't want to fool around testing right then. So there COULD be an issue there. Possibly. In my gut, I'm thinking it will probably be easy to sort out. Maybe.)
Of course, YMMV.
Supporting even a slightly different OS version is difficult for vendors, since there can be so many variables. USUALLY, they err on the side of caution, refusing to officially support a new OS version until they know for sure they're not going to be hit with a tidal wave of complaints. It can be frustrating -- particularly if most folks aren't reporting problems -- but it's simply self-preservation for the companies.