you say that MS are releasing every 3 years, but I can't see a gap bigger tan 2 years on the timeline that you put down.
windows 7 goes on public release in 11 days.
some people have been using RCs for some time so already know what it looks like.
i've got the full version on the laptop I'm using now, (because the company I work for already has it). I upgraded at the start of last week, though I was a few weeks behind most others in the company... visually to me is seems exactly the same as vista.
I think that MS are wrong to release a new Major OS every 3 years personally.
it doesn;t give people enough time to settle into a new os, so people may put off buying an OS, (like in 2003 XP had been out 2 years, but windows 98 was still the worlds most popular OS. if they leave a bigger gap between OS's then the upgrade should be a bigger upgrade, and be more worthwhile, and not leave people feeling like they were short changed on their last OS purchase.