I'm running Eckmuhl, Leipzig, Bautzen, Waterloo, 1814, and Austerlitz on both Windows 7 and Windows 8 machines.
<rant>I hate Windows 8 with the burning fire of 1000 suns. If I wanted something to run an operating system with the look and feel of a tablet... I would buy a freaking tablet. </rant>
I had one issue with a Waterloo game on the Windows 8 machine a few months ago. Changed the installation to a custom file path, like Mark said above, and have had no issues since. When you use the custom file path, you just have to make sure that when you do install patches, you change the file path they unzip to by default. I made that mistake once. Couldn't figure out why my game wouldn't update.
Recently had a bit of an issue in an Eckmuhl game, but that was a multiplayer game with 9 players. Kind of tough to narrow it down to Windows 8 with any certainty.
I've completed 7 different games with 4 different opponents in Waterloo since July with no problems.
I have had no other problems with any of the other games.