At first we thought Intense Debate was great. It allowed our visitors to comment without having to create an account on our site. The spam filtering while not perfect was good enough that we didn't see any big problems.
This plug in is a disaster. Don't install it unless you're willing to live with down time. On three separate occasions the blogs we manage suddenly had very sluggish performance - making them appear to hang.
At first we couldn't figure it out.
Then we started to compare notes and found the blogs using Intense Debate all either slowed or appeared offline during approximately the same time.
The plug in was doing this.
For some reason if Intense Debate is unreachable and you have more than 10 comments - you're site will either slow to a crawl -- or worst case go down entirely and become unreachable.
We had a LOT of patience over a lengthy two months before we dumped this stinker and went to Disqus which has been trouble free.