Your /data/app directory needs to be empty at boot for the mount to work. Either move the files with a shell command or wipe and restore.
Thanks tdm... third time's the charm, I guess. Did a full wipe & restore, since I wanted to get current on the nightlies... and it appears everything is now working great. No idea why I couldn't get it working before, but as long as it's on now, all's good.
Thanks for your continued efforts. Now if I could just get my Evo 4G running ICS as smooth as this Optimus S...
