One thing to think about if you to go Mac and then use Boot Camp to use Windows as well is that you are limited to 32-bit versions of Windows and all the crap that entails. I've just installed Windows XP SP2 on my 4GB MacBook Pro and Windows can only see 3GB of it because its 32-bit or some such reason like that.
I hope Apple will write some 64bit Windows Drivers so I can switch over to an XP x64 installation and actually be able to make use of all my systems resources and capabilities.
So if you are likely to need heavy weight full 64bit or massive RAM Windows capabilities you might either want to go with a dedicated Windows machine, hope for Apple to release 64bit Windows drivers, or explore Mac based alternatives or possibly even UNIX based alternatives. Afaik 64bit UNIX variants should be alright.
You could multi boot OS X, Windows (Boot Camp) and others with
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