Disqus seems to be working very well for us, and it solved the (SEO backlink) spam problem by allowing us to completely shut down creation of new user accounts. I doubt that it would be an acceptable solution for forums, as you wouldn't have all the features (ratings, threads, post counts, etc) readily available to you within CS. For just the few blog comments we get, though, it has eliminated the headaches caused by user creation spam (not so much comment spam itself, but users created to allow backlinks in profiles)
The particulars of incorporating Disqus into CS have worked very well, too, and Disqus has been making progress on speeding up things on their end. So yes we are completely satisfied.