not many. actually, with the move to intel, we should see the software barrier breaking as time goes on. boot camp already allows people to run windows. i don't know why anyone would, but that's my bias!
i've been on macs for years. i can do pretty much anything on my macs that others can do on pcs. the only exception is if you have an industry specific application that only runs on one platform. but that should change if apple continues to incorporate support for windows.
the best thing about macs is that they come with a lot of good software preinstalled, stuff you don't need to buy and most of it integrates with each other. and it works, too. apple has the advantage of creating both the hardware and software. it's a free for all with windows.
iphoto rules because you don't need to mess with installing drivers for your camera. you can produce your own promo videos with imovie and idvd. and publish it all with iweb. macs are the perfect tools for joining the media revolution.
apple also has awesome support, especially at the apple store. computers are complex and that means there's a good chance they will somehow break. i've been very pleased with how the apple store has handled my repair.
go over to apple.com and have a look at their current offerings. i say go apple all the way!