In case I forget here’s how to kill zombie processes (of which many seemed to be spawned, in particular by Chromium, on my Ubuntu 11.04 desktop):
kill -HUP `ps -A -ostat,ppid,pid,cmd | grep -e '^[Zz]' | awk '{print $2}'`
I’ve added this as an alias called killzombie. (Via here, plus multiple other sources).