I too was worried about the PHP requirement and Ubuntu. But now I run on 9.10 (October 2009) which works fine with Moodle 2.0 Alpha, and the LTS version of Ubuntu (which many sites will insist on running) is scheduled for April 2010 (10.4) which might even be enough time for Moodle 2.0 to get through the Beta stage, so if one is running the latest
server OS, one will probably not need to use alternative repositories.