As much as I would like to avoid seeing this blog turn into an Ubuntu complaints forum, I have another heads-up to share: Network namespaces support was silently removed from Lucid in a minor kernel update this summer (2.6.32-31 – 2.6.32-32). I just spent an hour debugging why Mininet had stopped working on my development VM. Downgrading to to the insecure version 2.6.32-31 solves the problem (ok for this firewalled development box.)
There is a corresponding bug report in Launchpad that has been confirmed but unresolved since May 2011.
