Apparently changes in the way they do rewrite rules on the new server has also broken commenting, and I haven't yet figured out how to fix it. As a result, I need to seriously consider migrating the blog. The two options are to switch to Movable Type 4.0, which requires some reworking of templates but shouldn't require any changes to archive paths (a critical part of this), or to bite the bullet and jump to WordPress. My only concern about the latter, without having done any research at this point, will be preserving the permalink format for my five years' worth of entries. Ugh.
So, commenting is on hiatus until I figure out the next technical step. Sorry. :(