I just got my IntenseDebate beta key, and have it running on my blog now. Random thoughts follow:
Installation was a dream. It was literally: install, activate, wait for converstion, and you're done. No tweaking.
It's purdy looking! Integrated with my theme with no effort on my part. Nested/threaded comments are awesome. Ajax comments, comment ratings, comment sorting (by date, by rating), integrated comment profile... all very cool.
It doesn't play well with CommentLuv.
I imagine that when ID becomes stable, CL will catch up. CL is disabled for now.
The comment management interface is pretty nice (with built in email reply and comment management), but I liked the wp-comment-remix interface better. There's a weird page within a page in the dashboard for managing comments, I don't like that part. I imagine that they'll work at a better interface once WP 2.7 becomes stable.
Overall, I dig it.