There is a mailing list for discussion of WebKit open source
development at firstname.lastname@example.org. You can sign up for
the list here.
If you would like help with development of an application using WebKit (as opposed to
development *of* WebKit), the right list is at email@example.com
with archives here.
You can find WebKit developers, testers, and other interested
parties in channel #webkit on the FreeNode IRC network (irc.freenode.net).
You can report new bugs and monitor the state of existing bugs in
the OpenDarwin Bugzilla,
in the WebKit product.