I have to say, I'm starting to warm to the idea of running Win XP and OS X on the same machine, which is wrong!
Initially I was like, no way! Being able to dual-boot a mac, sure it's cool, but I'd rather have a seperate PC to run Windows on, but I'm gradually being swayed. I'm currently eyeing a 20" iMac as my next computer purchase and being able to ditch my ageing 750MHz K6 PC in favour of having one computer is pretty cheers.
Plus I REALLY want Age of Empires III, which; a)isn't available for mac, and b)would cripple my PC.
I think the thing that would really swing it for me and I think could make a cool addition to Leopard would be to integrate the whole Boot Camp thing into fast user switching, THAT would be cool! w00t!
I know most people want virtualisation, which would also be pretty cool, it all depends on what u want to run. For running Windows apps that aren't available on OS X, or in a situation like at the moment, where there isn't yet a universal binary for Photoshop (et al), virtualization is fine, but full on games, if they're Windows only, it'd be easier (and probably better performace wise) to boot into Windows for them, if you can do that without completely re-booting the machine CHEERS!