You can subscribe to the Gnumeric listserv at http://mail.gnome.org/mailman/listinfo/gnumeric-list. Please note that, to prevent spam, only subscribers may post to the list.
There are generally some developers and users around on IRC. We can be found on the IRC server at irc.gnome.org, port 6667 (standard IRC port), on channel #gnumeric. If your browser supports it, you can click on this link to go there. Please be patient if nobody responds immediately; many of us lead busy lives!
For general queries, the webmaster for www.gnumeric.org is best contacted through the Gnumeric mailing list. If need be, direct mail to mwelinder-at-gmail-period-com will reach me.
As always, patience and politeness will help in getting assistance. Respect the users and developers, and they will respect you.