I have used the Surface extensively the past several days and here are the biggest issues I have experienced so far:
1) The speakers are very soft (not loud enough). I have it maxed out at 100 and can barely hear the sound if the Surface is more than 2 feet away. My Lumia 900 (or my wife's iPhone) plays youtube videos much louder than the Surface. I really hope they can fix this.
2) Type Cover stops working randomly. I have to detach it and then re-attach it for it to work. I don't have a Touch Cover so I can't see if it affects Touch Covers as well.
3) I'm a very fast typist (approx. 125 wpm) and a lot of times, the Type Cover can't keep up. When I'm typing (such as this post), all of a sudden, none of my keypresses go through. I have to stop for a second and then it starts working again.
4) The Mail app - EAS (Exchange ActiveSync) options don't take effect when adding more the several accounts: I have 5 different email accounts enabled in the Mail app, all of them are Google Apps hosted. Therefore, like my WP7, I am adding the accounts using the "Outlook" option so I can use EAS. The 4th and 5th accounts, the "Download new email -> As Items Arrive" option does not come up. Therefore I have to use the "Check every 15/30 minutes" option which is less efficient and uses more battery, from what I'm told.
5) WiFi connection get sluggish/disconnects randomly. I have to either reset the WiFi connection (by turning on/off Airplane Mode) or just reboot the Surface to make it work again.
6) Internet Explorer (Metro): Pressing (via touchscreen) links on web pages sometimes don't work the 1st time. I have to press the link multiple times for it to actually work. Seems like an IE10 bug/glitch with touch input.