Morbus Iff, extensive technical writer published with O'Reilly, maintainer of disobey.com, and the author of AmphetaDesk news aggregator, has put together a PHP import script which does a detailed conversion of MT into Drupal. From the import_mt_README.txt:

This import script was created so that converting from Movable Type
to Drupal wouldn't be as difficult as these things normally are:

• Movable Type authors are imported and given a random password
  (for them to login, have them "Request new password" - they'll
  receive it at the email address associated with their MT author).
• All Movable Type entries are imported into Drupal nodes.
• Your Movable Type categories are imported as a Drupal taxonomy.
• All comments are imported as anonymous user comments (ie. no
  user accounts are created for your commenters; as such, comments
  they've left before signing up for an account in your Drupal
  installation will not be associated with their user).
• Trackback data is imported (though, by default, Drupal doesn't
  come with trackback support outta the box. similarly, I've not
  tested this feature heavily, as I don't use trackbacks myself)
• Your MT permalinks are aliases to Drupal nodes, such that no
  linkrot should exist when you delete MT and enact Drupal (see
  below for usage instructions)

With DrupalBlog, I've enabled the story module that the import script uses, as well as the path and trackback modules. So, I believe this script should work with it to quickly convert over an MT site into a working Drupal blog site. I should probably include links to it in the documentation.

UPDATE: Morbus Iff let me know that the script is meant to work with Drupal CVS, not Drupal 4.4.1. So it won't work with the current stable release of Drupal or the DrupalBlog dist. That is, unless the anonymous commenting system is backported to 4.4x.