Honestly, I don't see much use for MacOS X. MacOS X is supposedly better for multimedia and Windows is supposedly better for gaming. You can't do hard-core gaming in MacOS X but you can do hard-core video editing and graphics in Windows Vista just as good as you can with MacOS X using Adobe CS3. Also, Encoding any tv or dvd rips is a lot better on Windows Vista than MacOS X or Linux. In reality, you can do just about anything on Windows Vista except for a decent server which is where Linux comes in with MythTv, NAS, and a bunch of other neat server stuff.
PS: MacOS X has issues too, the fact that my laptop won't take MacOS X Leopard and it meets the minimum requirements for it. Apple hardware is pure garbage and I got MacOS X on an Intel Core 2 Quad Q6600 for around 600 bucks and it outperforms the most expensive iMac.