I just downloaded the twrp source a few hours ago so this is TWRP V126.96.36.199. Unfortunately, the external SD does not mount but I did manage to get adb to work. I think that you could always adb push a rom zip in the event you cannot boot, forgot to make a nandroid, and forgot to have a "just in case" zip. Also, when rebooting, YOU MUST CHOOSE REBOOT SYSTEM. If you just poweroff, it will reboot into recovery the next time. If you forget and choose poweroff and it reboots into recovery, just choose reboot system and everything will be fine.
Attached is A1 (the character my A1 kernel is named after) holding my I9300 showing the recovery. The source is also uploaded, which includes files that I've changed in case anybody is interested to know how I did it. There is a rootzwiki page with instructions I followed. Just a few minor deviations from the instructions. I did "make recoveryimage" instead of "make amp amp..." that they recommended. And the obvious deviation, our device is called i9300 not tenderloin. That's the HP Touchpad.
I flashed the latest CM10 nightly from it, the latest siyah kernel and a touchwiz zip and nothing went wrong. Also tested backup and restore. Went fine.
Here is a youtube video demonstrating TWRP on the Galaxy Nexus by some random person on youtube.
Credits: team win, siyah kernel developer (recycled your zip to make the recovery zip). None of the code is original from me. I only tweaked the recovery.rc to enable adb.