I find running a vm (using parallels) of windows 7 has little effect on battery life over just running OS X. I think that's because windows isn't having to deal with the hardware.
I wouldn't use Bootcamp, these days, on a Mac unless I was gaming when you really need to take advantage of CPU and RAM
Windows XP loads in about 8 seconds on a 5400rpm MBP 15" so imagine how quick on a 2011 MBA!