To get the Dev options (and Perf) back you need to click 7 times on the Build Number in "About Phone" -- it's hidden and will prompt you with "x taps remaining" as you go
I also have the problems with Superuser -- FCing when prompted for access but seems to work once set (root apps all work). I think it's a perms issue but I haven't looked closely at it yet...
I had a more horrifying issue as art of this upgrade -- lost my IMEI !
Happened after I downloaded (but NOT installed) 10.1 via the CM Updater. I just saved it to local storage and was going to reboot into Recovery to perform a backup first. After backup ran, IMEI was gone -- and backup was corrupt as well (incomplete).
Though I'm not sure it is 100% related -- since missing IMEI does seem to happen randomly on GS3 models from what I hear.
Fixed though -- and running like a charm (I flashed 10.1 after fixing the IMEI)