I am the tech lead for Goobuntu, Google's in-house derivative of Ubuntu, used as an Engineering desktop amongst other things.
I'm also a Debian Developer, my packages are listed at http://qa.debian.org/developer.php?login=apollock
My current involvement with Ubuntu is bug triaging, and reporting Enterprise-level bugs that we encounter in Ubuntu. We're mainly interested in the LTS releases of Ubuntu, but we also follow the other releases. I'm interested in becoming an Ubuntu Developer, so that I can directly contribute to bug fixes that affect us, and will no doubt affect other large-installation, large-scale customers.