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.