Consensus view seems to be a June / July 2009 launch of Windows 7.
Given that it's an evolution of Vista, and the reaction to the betas have been pretty positive, I'd say it'll be pretty much OK from day 1.
Of course, many will always wait for SP1! But I think that a huge number will skip Vista SP1 and go from XP to 7.
MS really cannot afford another lemon like Vista.
SD