You did not mention an SDK version.
Ubuntu 11.04 with 11.6 driver and 2.4 SDK are the sweet spot for me.
It does seem odd that the miner would hang instantly, there are some functions that are done before mining starts that take a few seconds. Did you install pyopencl and python-jsonrpc?
https://bitcointalk.org/index.php?topic=7514.msg110334#msg110334Sorry, I should have put this in the OP. It is 11.6 and 2.4 SDK.
I took the machine apart entirely this past weekend and put it back together and now everything is working, at least for the moment. Hopefully it was just a loose connection somewhere in the box.