On any computer, I use suspend or hibernate to avoid having to boot. Linux isn't going to boot up any faster than a clean xp install. I'm curious, did you do an upgrade or a clean install to 7? Doing an upgrade usually brings over all the baggage that was making the last version slow. Without getting into a 10 page dissertation on how bad programming/hardware makes windows much worse than it should be, suffice it to say, a well tuned windows machine should run very fast.
I'd like to think I'm not partial as I own machines with OSX, Ubuntu, Debian, and XP. Each one of them has their own problems. I think you might get frustrated with Ubuntu's learning curve if you have to install software that isn't available in a connected repository or mainstream enough to come as a .deb package (ubuntu uses debian as its core) New hardware will be a bit tricky to get drivers for too.
The best part of ubuntu though is, you can install it as a dual boot, it will re-partition your drive and install a boot loader that will let you choose which OS you want to load at bootup. Its easy enough to get rid of it too.