It is quite good if you have a tight content niche and make all your links no follow. This will get rid of many of the spammers and can really help with long tail searches. Avinash is a huge fan of this on his blog and he even keeps a metric on the ratio of the words written by him vs words written by engaged audience members.
But, you need to be the one driving the conversation and setting the agenda, if you don't you will just get spammers and junk on there. Best of luck and feel free to PM me the blog, I'll check it out.