Expose / Space / iPhotos / iTunes / .mac - theses and many other features (and 3rd party apps), which works very well together with each other, gives it an overall better feeling than what I can get from Windows. So in simpler words - OS X > Windows IMHO. If I can run OS X legally / properly on a decent Windows system (or a better laptop than my MacBook per pricing) - I'd happily revert back to PC.
P/S it's not just about the GUI, the independence of Apps and System files is a plus for OS X than Windows.
Maybe it is just me, but, why do you need iPhotoes to work with iTunes or Space? or anything else? What exactly do you mean by it works better togethor?
There doesn't seem to be any tangible reason to get a mac, that is my current opinion, but I want someone to convince me otherwise.