The installation went smooth. I chose to "keep everything", and I didn't lose anything after the upgrade, as far as I can tell.
The biggest problem for me, though, is that my Roland UM-1 no longer works. I downloaded the Windows 8 driver for it, but still, for some reason, Windows doesn't even detect when I plug the UM-1 into my USB port (I've tried all the USB ports). I'm not sure if my UM-1 is simply broken, or if it's a compatibility issue. I tried connecting the UM-1 to a different, Windows 7 computer, and Windows saw that I had plugged it in, and said it was installing the device drivers for it, but the lights didn't go on on the UM-1.
I use the UM-1 because I have an M-Audio Axiom keyboard, and the USB from it barely works.