I have been an OSX user for 3 or 4 years and basically own one machine in each segment now (including a recent mini as music server). I am overall very pleased by the value provided.
I still use Win7 at work and I do like it as well. I feel that MS has progressed a lot more than Apple on the OS front in 3 years. Tiger was miles ahead of Vista but Snow is only marginally better than Win7.
One major concern with the Mac platform though is the lack of focus of Apple on the high end. The Mac Pro has only seen very shy upgrades these past few years and is getting technologically outdated in terms of memory capability, interfaces,...
I am also not sure to like where they are going with the Mac App store. Jobs' big brotherish views are getting old and I, for one, was shocked by their decision to remove the Wikileaks app from their store. I don't expect my solutions providers to either propose political views nor to act as gov puppets.
So all in all, great user experience, but there are clouds showing up on the horizon...
Cheers,
Bernard