I've seen a lot of different sites using it. I haven't implemented it personally on any sites so not sure if it increases the activity.
I found this though:
http://www.quora.com/Which-results-i...omment-systems
And this guy said:
http://www.webgeekly.com/lessons/5-t...-blog-traffic/
If anyone’s been following my blog since the beginning, you’ll be aware that I have tried many different solutions for comments. I moved them to the right, made them stick to the page as users scrolled, added notices in the post to encourage posting, switched to Facebook Comments and finally removed all the fancy features and switched to DISQUS as they are now. Getting comments isn’t easy. Even when you get quite a few visitors, you’ll still find that an extremely low percentage will actually comment. Having tried so many different variations, DISQUS is definitely the most effective way to increase comments.