Don't forget this is how it usually is, we had windows 95, then 98, then ME (despite the fact everyone would rather forget it existed...) the 3 year release cycle does seem to be the norm, it was just because Microsoft crapped up Vista so much everyone seemed to forget it was like that!
I'm personally not against a 3 year release cycle so much, but I am against anyone who tells me I need to upgrade whenever a new OS comes out and tells me to "get with the times". Same goes with any product really. I'm in the camp of those still using XP, and not planning to move out yet! Don't forget there were still huge numbers of people running windows 98 when XP was launched...
Perhaps windows 7 will be the OS we've all been waiting for, perhaps not. But I see no harm in being cautious at least for the time being before everyone jumps on it. Yes, initial findings do look good, but they are just initial findings. We'll only be able to tell whether it's as great as it seems for certain when it's been rolled out large scale across the globe and had a chance to settle in and prove itself. THAT'S the state that I'm waiting for before I take the plunge.
As for windows 8 and beyond, there's nothing wrong with working on that up front. It's not that Microsoft are already planning to scrap 7, they'll still have teams of people working on security / bug fixes and the like, it's just the reality of being in one of the largest companies on the planet (especially in the IT field) - you have to plan many years ahead to make sure you stay on top of the game!