I switched because:
1. STABILITY - OS X's stability is unmatched in the consumer OS world.
2. PERFORMANCE - Macs really do JUST WORK. Sure, there are issues here and there, but they take less time to fix than they would on a PC.
3. STYLE - Everyone knows Apple is an innovator of product design. Just look at the iMac, Mac mini, Powermac, Powerbook, iPod, etc.... There's something to be said about being able to work on a machine that both works well and looks fantastic.
4. COMMUNITY - Mac users are part of a worldwide cult. A cult that has answers to every problem, question, or concern about Apple and its products. There's something to be said about loyalty to a product because of both service and value.
5. SIMPLICITY - OS X is incredibly simple to use. Within 5 minutes, everything is ready to go. Intuitive GUI and accessibillity makes it shine.
Those are just a few reasons. Some are against Macs because of incompatability with gaming, etc. I would say the majority of Mac users are those who are creative, intelligent, and are not afraid of going against the grain. If you want to play games, buy a gaming console, or a gaming PC - that's what they're designed for, gaming. The Mac is designed for something on a much grander scale IMO.