To be honest I think desktop replacement laptops are a waste of time, I've got one and it's shit. far too heavy to carry to class, runs stupidly hot and it's far more expensive than an equivalently specced desktop.
Mac's aren't bad, they're relatively light, and very well made, but you're paying a premium for them, and frankly, they don't do anything a cheaper windows setup can't do.
I'd stay well clear of IMac's if you want to do anything that needs good colour precision, you're stuck with a glossy screen, which sucks.