I've now switched over to Blogger comments. In order to keep the existing comments from earlier posts, I've included an "old comments" link on each post as well. Ideally, I'd like to remove that link on new posts while leaving it intact on old ones -- but I couldn't find any way to do that.
If any tech-savvy reader out there can think of an elegant way to do what I want, please let me know. Here's a start: My Blogger template includes tags that look like [BlogItemCommentsEnabled] and [/BlogItemCommentsEnabled], which surround the link for Blogger comments. These tags make sure the Blogger comments link appears only if I've enabled comments for the post in question. So if there were some kind of "not" operator, which would have the effect of a [BlogItemComments-NOT-Enabled] tag, I could use it to make old comments show up only if Blogger comments had not been enabled for the post in question.