If you want to write a longer comment, send patches or similar thing, the best way is probably by using the pingus-devel mailing lists, subscribe information can be found below, to just send a mail to the list write to firstname.lastname@example.org.
There is currently no pingus-users mailing list due to the lack of traffic, so using the pingus-devel list for questions about the game is perfectly ok.
If you want to submit a bug report about Pingus or simply browse the list of open bugs, you can do so at the Pingus Issue Tracker. Submitting stuff there should make it sure that it doesn't get lost.
For a quick help you can try the IRC server irc.freenode.net:6667 and the channel #pingus, you can find the project maintainer (nick: grumbel) there most of the time. From time to time there will also be IRC Meetings with larger parts of the development team, once such meetings happen, they will get announced in the news section.
If you don't like IRC, there is also the possibility to contact us directly via Instant Messaging.