I use Windows sometimes on my Mac for software that does not have a Mac version and I need for my job.
I have two laptops, one MBP and an ASUS and basically I use the Mac for work and the PC for fun. To me it is the perfect combination. I have the power of a Mac combined with the flexibility and software offer of a PC. Actually I had two Macs for a while and had to sell my iBook to get the PC: streaming was hell most of the time because of the lack of compatibility, some video codecs or programs were not available, reduced game offer, etc.