actually windows 7 has had alot, the kernal has been significantly re-worked, the memory management systems have been tightened up alot, the driver model tweaked etc etc.
Just because it hasnt had a mind blowing visual makeover, peple dismiss it as small upgrade, bit silly really.
And i never said vista was pants, I loved vista to bits, it was everything an OS should of been, but so far, windows 7 seems, well, better, in every way tbh.
Not sure about SLI support yet, the nvidia drivers are only betas atm so now wouldnt be a good time to guage that kinda stuff, always takes a while to get drivers sorted.
With regard to OSX, what does it do that windows doesnt? I look at OSX from a typical consumer point of view, yes I'm a power windows user and I know what im doing in windows etc, but OSX ticks none of the boxes for me, its an OS that doesnt do what I want, running on the same hardware.
On a side note, thier mac pros are insanely priced, i could build a far better specced pc for quite literally half the money, and have change from that no doubt. I think ur paying for the badge tbh.