I have Windows 7 on my MBP and use it about twice a month. I purchased it to program a universal remote that cost well over $500 and required Windows for the programming software. I also use it now to run the Blackberry Theme Studio (yes, I unfortunately still use a Blackberry...can't afford to get out of my Verizon contract yet). I'm not a big PC gamer, but its always nice to have the option to run Windows for games too. On occasion I use it to troubleshoot for friends and family who are less tech savvy.
Honestly, I would say if you don't absolutely have to have it in order to run a crucial application (like that remote software, for me at least) that will not run in WINE (Google Winebottler for more info. Most basic applications will run in WINE, but those that require driver installation generally have difficulties), don't buy Windows, it's really not worth the hassle. I have spent a good 5 hours getting my Windows partition set up and it's still not exactly how I would like it. It's not like Windows is any better than OS X or we wouldn't be at this forum 😉.