well let's see...
1. you don't get a right-click function like someone else said.
2. A LOT of the keyboard shortcuts are different.
3. for pc users, a TON of their programs and software will not work.
4. some documents and files can only be opened on the pc.
5. a lot of multimedia files, like wmv's, can only be played on the pc.
6. you have to buy more software to fill in for the pc ones that dont work.
7. you have to learn how to use a whole new interface. (trust me, it's frustrating when you don't know where things are)
8. a lot of the peripherals that macs offer are intensely overpriced...firewire and usb cables are $40 at the local apple store.
9. oh and network troubleshooting, like connecting to a dsl network, can be a pain when the network is pc based.
10. but all in all, the only difference is that macs cost more to do the same things.
hope you have fun with the macbook.