Good point, maybe I've been lucky so far, I got into it in a roundabout way from a beta reader I found on Goodreads. She is very good, but only does sub-6k word segments. Critting other people's work is a great learning tool, although actually applying it to my writing is another skill I'm only just starting to acquire.
I've also found you can join too many communities, two is plenty (JW and CC). More, and it gets in the way of writing, which is not the idea. Beware of online displacement activities, and get back to the real writing! :)