First, thanks for your hard work!
I've updated my Ubuntu 12.04 x64 today and since the reboot cgminer 2.9.* creates coredumps.

Version 2.8.7 is working fine, 2.9.3 and 2.9.4 are not. The core dump is created randomly after 1 to 30 seconds after cgminer was started.
This is the gdb output:
May be the same problem than the one I reported on IRC (and started for me at 8AM GMT today), if it is, adding --fix-protocol should be a temporary fix (it disables the switch to GBT protocol).