Some time ago when I first installed Intense Debate I inadvertently cause it to overwrite the Blogger comments that were there prior to its installation.
I mulled over whether it bothered me to lose those comments and ultimately decided that it did. In many cases those "lost" comments added a lot of life and spice to the post itself so it made sense to me to uncover them so that they could continue to "do their job."
I haven't decided yet if I am going to re-install Intense Debate but if I do I will make certain that the old comments aren't covered. In the interim I need to see if I can export comments made in Intense Debate into Blogger.