We recently had a mishap while trying out IntenseDebate integration on our blog. While importing all our existing comments, it marked all spam comments as approved. It left us with over 6000 comments out of which over 50% were spam and we had no way to separate them from the legitimate ones. It was a disaster. We finally fixed the issue by using Akismet and some simple SQL scripts. If you have a similar issue, this is something that may help you. http://woikr.com/howto/accidentally-approved-all-the-spam-comments-on-your-wordpress-blog-here%E2%80%99s-a-fix