I'm running my own build of this at the moment, with support for the P990 enabled. I tried installing SuperSU instead of Superuser, and everything loads perfectly well on boot. The rom I am using is just stock v30a rooted with su though CWM, and not a custom one.
I spotted a post from Rohanajoshi in the DjangoManouche ICS thread saying there was a problem with superuser: apps dont get root access when settings are like "automatic response => Allow"
SuperSU solves this problem and lets the service run properly on boot. So if you're on the topogigi rom just download ergosum's first version and it should work.
I spoke too quickly there. I had problems with SuperSu for a bit and broke the app completely. Managed to fix SuperSU, then a reinstall of the app and everything works great