I put 7 on my laptop sometime around the end of M1, I moved my development machine at the end of M2 and I moved my home machine at the end of M3 (every Monday morning I upgrade my laptop to the most recent build, every Wednesday
morning I update my development machine to the most recent build and every Saturday I upgrade my home machine to the most recent stable build (as determined by the build lab)). I followed more-or-less the same upgrade cadence for Windows Vista
Because he's been nagging me about it for months, I upgraded my son's machine from XP->Vista->Win7 Beta last week.
So far I've been pretty impressed, to be honest. There have been a couple of glitches here and there (for instance back in September there was a period of time when some fairly popular games would blue-screen the machine), but in general Win7's been pretty
Of course YMMV. I intentionally live on the utter bleeding edge of dogfooding and my machines are all backed up daily so if something goes wrong I won't lose too much work.
My work desktop, home desktop and netbook are running the beta. My work laptop is running the most recent build of our dev branch.
Working in Vista (or XP, eww) feels just wrong now