Ive been trying the win 8 X64 developer preview with Cubase SE and Acid Pro 7. So far so good. I want to say best yet as far as Acid performance. Cubase SE runs best in XP mode.(same as when using in vista and 7)
As far as a basic OS- 8 seems a little snappier than 7. The new start screen is probably handy for phones or tablets but Ive switched to booting directly to the desktop.
There was a video driver prob but that was specific to the Dell M65 with vistaX64 and 7X64 as well.
Running Massive with no latency adjustments needed. Acid has gotten better re softsynth stability/latency but Im not used to loading several instances of Massive without having to increase the buffer a little.
The disclaimer of course is that this is a fresh instal and once all the plugins are loaded and I open a "heavy" project that would normally require track freezing, turning off fx etc...that will be the real test.
At any rate I can report that AP7, Cubase SE and Ableton Live 8 Lite run fine.
(AL8 also wants to run in xp mode. AP7 seems to do fine without compatibility settings changes.)