I've only had Windows 8 running for a few days so still "breaking it in". I did an upgrade from Win 7 Pro 64 bit - and pretty much everything works fine.
I've found that if anything *doesn't* work - just uninstall and then reinstall. I did this with Kaspersky Internet Security 2013 (metro tiles didn't work until I reinstalled) and my MOTU USB MIDI driver. Also I had to reinstall a printer driver for my Canon Printer (on my "non music" partition).
Other than that - everything seems to work fine, but I'll let you know if that's not the case.
EDIT: I stuck start8 on too. It's handy and only $5.00. It gives you your start menu back...