Just got mine updated from CM10 to 11 and man, what a difference! It went from barely usable to very usable. Which is really an added bonus, because I really only use it for reading. I just like upgrading stuff. This is how it went for me. I had CM10 with TWRP installed to EMMC. I put my microSD into my Surface, downloaded the CWM update zip, CM11 nightly zip, and gapps zip for CM11. Put all zips on the root of the SD.
-Loaded up in TWRP recovery mode.
-Chose install. Chose the CWM update zip.
-Rebooted and chose EMMC recovery. It loaded up CWM.
-Chose install again and installed CM11.
-Rebooted and chose EMMC recovery.
-Installed gapps the same way.
Bam. So I didn't realize it at the time, but this actually did an upgrade instead of a clean install. All my apps are still there. I might want to wipe and do a fresh install, but I'm not sure how. I didn't think this would preserve everything. But I'm happy with it. It had a few hiccups loading Clash of Clans and Facebook the first time. But after updating the apps to the latest version and clearing data and cache, it seemed to fix things.
Kudos to the CM team!