I have a Macbook Pro. Firstly, we need to lose some of the stereotypes.
- macs aren't much better than a windows machine for graphics designers
- they are totally compatible with files created on a windows machine
- not all software is available and exactly the same for macs, but most 'big' software (word, photoshop, etc.) is available for both platforms. any other software that is windows-only almost always has a similar product for mac.
- only real loss is lack of games for Mac OS X. Still lots there, but nothing like the array for Windows.
However, macs are enormously easy to get used to. Remember that Microsoft copied the Mac to make windows in the first place! They do do some things differently, so it'll take you the first initial few days to get used to it, and you may even get annoyed that things you do on windows is done differently on a mac. But often you'll find that the mac way of doing it is more logical, or just requires less steps and so is faster.
They also make you more productive, because you spend less time dealing with the niggles and more time doing work or whatever you actually want to be sat in front of a computer screen for.
If you live near an Apple store, then I strongly suggest you go there and try them out. Even better if you have a friend with one.
Note that mac users will almost always tell you to buy a mac, because they've gone through the same process and are better for it. Most windows users will tell you to keep using windows, since they don't know the hidden benefits of using a mac that can only be realised by doing stuff on it, and not reading a manual on the features or seeing a magazine article about them.