If you use Parallels, you can even set it up to talk to a BootCamp partition. I do this myself and I find it really handy as for most applications which you need to run in Windows you can just launch Parallels like a Virtual Machine and run Windows within OSX.
However, if you DO need to do something which requires the full power of your computer (for example play a game) you can use Bootcamp to jump into Windows only. I only have to do this very rarely but it's really great to have the ability to do it.
I'm not sure if the other VM solutions allow you to do this... (I'm sure that at least some would though, they all try and keep up with one another in terms of features)