I have been running a cluster (~10 nodes) of ISPC3 servers on top of Debian Squeeze for a couple of years now and I must say... It rocks.
As we say here in Finnish it's "Steady as a train toilet."
Meaning it's so simple it never breaks down.
Thank you all for your hard work on this project.
Every now and then I read about the problems people have with Cent OS, OpenSUSE and Ubuntu and I wonder... why do they choose all those problems for them selves? Forget GUI, forget .rpm, forget ubuntu (unless you use LTS.)
You are just asking trouble if you use those "newfangled contraptions."
IMHO = ISPconfig3 + Debian Squeeze and you sleep much better.