Things really do "just work", no tinkering. Your computer is like a car, you just "turn the key" and go.
Not targeted by viruses, spyware and other trash that infests PC (due to lack of popularity - if the Mac ever got as popular, it would be targeted and therefore might have virus and spyware problems too) however...
Much more secure, reducing the risk of viruses if the Mac platform were targeted.
Better performance for graphical design work.
Really nice interface.
Built on BSD with an accessible terminal for those with *NIX/BSD experience to have a further tinker, and all the advantages (very stable, open standards etc) that go with it.
Predictable, well-made hardware - no problems caused by you having a different motherboard with certain incompatibilities etc that you get with a PC.
Don't even get me started on the Powerbooks