Gmail voice and video chat plugin was installed successfully on Mac OS X 10.6.1 and works with Safari 4.0.3, Chrome 4.0.221.8, but is not loaded by the WebKit nightlies. "Googletalkbrowserplugin.plugin" appears in the plugin page for Safari. I am just a casual user of WebKit, and have been enjoying the speed and overall experience of the nightly builds, until I ran against this issue.
*** This bug has been marked as a duplicate of bug 30295 ***
(In reply to comment #1) Thank you! I don't know why I couldn't find it initially... It's working now, just needed an update.