I installed IntenseDebate on FirefoxFacts.com a few days ago, and thus far – I like it.  There are a few bugs and annoyances, but overall the product is really cool.  The idea here is to add tons of new features to your standard commenting system. 

Some of the cool features that IntenseDebate brings includes:

• Comment Threading – this allows you to add a comment to the general discussion, or just reply to one comment that needs a reply.
• Reply by E-mail – the reply by e-mail feature makes it super-easy to stay in the conversation.  You can respond to and moderate your comments with the ease of just replying to an e-mail.
• Importing and Exporting – the best feature of all, the import and export feature is nice.  It gives you a “way out” just in case IntenseDebate doesn’t tickle your fancy.

You can read about the other features, such as reputation points and commenter profiles here.   There is also a ‘bit of a social network thrown into the mix too – which is a nice touch.  You get your own profile page, where people can find where you have commented and who you are following. Here is my profile as an example:  http://www.intensedebate.com/people/cheasym

Sign up is easy (especially if you have an Open ID) and they walk you through the steps of adding it you your blogging engine of choice.