On my Mac Pro I run VMWare Fusion and XP Pro SP3 and it is fine for my work apps (data analysis apps). Virtualization has the advantage of having built in ability to share folders from the Apple native machine, so you do not need to allocate a large amount of disc space for the virtual windows machine. I use my OS X Users space for most of the files I need on the Windows machine, and just access them from shared folders (which appear in Windows as pseudo-network shares).
The problems with virtualization, over booting into windows directly, is that you give up some performance (especially video performance, as the virtual machine has to use drivers provided by the virtual machine to interface with your graphics card). Also, you need to have enough RAM to run OS X, load a virtual machine, and run a virtual Windows box in it. My work Mac Pro has 10GB of real RAM, so I actually have a 3.5GB Windows virtual machine running all the time, with still plenty of RAM available for OS X and its applications. On a laptop limited to 4GB, that could be a real limitation (although for those who can afford it, a new 17" MacBook Pro with 8GB would be fine). Depending on disc space needs (how much has to be windows native for your windows applications), a laptops hard drive could also be an issue.
So, I'd say you need to really nail down just what you need to do in windows and decide accordingly. If it is for games, then Boot Camp clearly seems best, as you would be booting into a native windows installation with direct access to all it's required hardware (no virtualization layer between it and the hardware). If it is for files that you wish to share with both OS X applications and Windows applications, then virtualization is better, IMO, as you can simultaneously use both operating systems, and easily move files back and forth between your OS X desktop and your windows virtual desktop.
Also note if you go for virtual windows, then VMWare Fusion is available form the Apple store for an education discount price (I don't know about Parallels).