Just a quick post with some links to people who said it earlier and better than me:
Also, this is a good idea:
https://bugzilla.gnome.org/show_bug.cgi?id=313147 so http://live.gnome.org/JhbuildIssues is more visible. Maybe add it to http://library.gnome.org/devel/jhbuild/unstable/index-info.html.en somewhere?
I know that building the bleeding-edge GNOME with jHbuild is not really necessary for people starting to contribute, but it's an experiment I wanted to do, and it serves a good purpose: I'm learning a lot on the way.
Maybe I will file some bugs when I encounter any clearly module-related problem, since that is another way to contribute.