If you’re a PHP user, you might want to follow the php-internals talk. But it’s a very talky mailing list. So, “follow” it. From afar. My medicine is to go to the web interface like once a month, and just look at the interesting headings.
“We have packaged PHP 5.3.0beta1! Go test-run your PHP apps. Should be interesting.
Also: “The PHP TestFest is a worldwide event in which PHP user groups and individuals contribute to PHP by writing tests for PHP.” Testfest at wiki and at the QA team’s page.
And, the PHP5 buglist.