I installed 8.1 on my Surface Pro. The Installation worked flawless.
One thing that i notice is that i can get my 5 tiles back. It sticks with 4, even after installing the 5 tiles hack.
The other one is that live tiles on the picture app is not working.
Didn't find any other issues yet.
At least it gave a sensible error message. TechNet forums have various threads - some say that a full wipe and reinstall selecting EN-US fixed it. I'm not sure I fancy a full wipe and reinstall just for the preview.