I have both 8.0 ( 32 bit ) and 8.1 ( 64 bit ) running on my win 7 machine. 8.1 seems to run fine, but I'm not really using it due to a number of issues with 32 bit drivers and plug ins. Namely, I've been putting off updating the ray light update, plus I have a bunch of old audio plug-ins
The Canon H264 loads fine in 8.1, you need the older quick time to use the Canon H264 with 8.0
Depending on what you are doing, you will probably be fine.
Strangely enough, I had the opposite experience. On my Win7 Ultimate 64bit, Vegas 8.0 went wacky one day. I reinstalled 8.0 and it was still acting up and not rendering correctly. I decided to uninstall 8.0 and install 8.1. It's been flawless ever since. I guess YMMV