I made my bootcamp partition 90GB. I mostly use it for games only and wanted to give it enough room for a few games to be run from the SSD (with the rest on a USB HD). You can shave off over 20GB (or more depending on your RAM) by disabling system restore, hibernation, and the page file. System restore is useless.
If you're savvy enough to install Windows on a Mac, then you are the kind of person who has no use for system restore. It's meant for mom and dad and even then it's not very good. Windows probably isn't your primary OS, and even if it was, hibernation sucks. Compared to sleep, it would be better on battery and if you're running on battery it would be nice to hibernate to save your work before it runs out. That would only affect a minority of people though. Hibernate is slow, booting from the SSD is fast as it is. Disable it.
Disabling the page file is a debatable topic. If OSX is your primary environment, it's probably worth removing. 8GB is plenty for 2012. If you're the kind of person who uses windows a lot and does a ton of multitasking (or uses the windows version of photoshop which requires it), you might need it. That's not most people. Most games are 32-bit too and don't even use more than 4GB of ram. Some rare programs and games require it. In my experience, it's fine.