I’ve commented on it a bit elsewhere so I figured it was time to throw my two cents in regarding my experience with it.
So far, I have had no programs actually break from it on my laptop which I use for all my work.
At least I should say none that broke un-intentionally. StyleXP broke right after I installed it — which was right after it was released on the MSDN download site. But it only broke (to my knowledge, they have claimed it worked SP2 for a while) because the version number in Windows changed.
That said, the only games I’ve played on my laptop have been of the flash/shockwave variety so I can’t comment on that yet…I’m waiting until I can do a full backup on my gaming PC before I install it there.