IRC

There is a non-developer #flickr channel on freenode.net.

Richard and sometimes Cal can be found in #xulrunner on irc.mozilla.org.

If you want to talk about Uploadr, #flickr on irc.mozilla.org might be a good place to start.

Forums

The code.flickr.com forums are a good place to whine about Flickr development. You just need a Flickr account to get started.

Mailing list

The Flickr API has a dedicated mailing list for questions and discussion.