Email discussion lists and comp.lang.scheme are an excellent to start.
Another option is #scheme on IRC at Freenode; there is nothing like speaking to another human being about Scheme.
When you talk with folks; you learn faster and have a lot more fun. When you are really digging into a concept, the kind soul who answers your question at just the right moment can make the difference between learning the concept now, or in a few days. Not to say that learning is a race; it is just so much fun that I think everyone loves to learn the next thing!
An aside; I’ve found that my mastery of topics, and in particular the lack thereof, is revealed much more quickly to me when I open my mouth! I won’t miss a chance to do so!