I've used Wordpress on and off for several years to power my rambling about code and work. It has served me well and I think offers some advantages over more robust platforms (mainly that it is a fairly refined tool for blogging) for straightforward tasks like blogging. This being said, wanting to showcase some of my work on Drupal a bit more clearly, having a major data loss last month, and needing to get more acustomed to Drupal 6 have made the proverbial push over the cliff to move to Drupal from Wordpress easier to stomach.
Poking around, there seem to be many ways to upgrade from Wordpress to Drupal. Having a fairly straightforward site seems to help- I had pretty much a single user setup with only blog entries, pages, and taxonimical data. After trying a few things out, I settlled on using the Wordpress Import module.
The downside to this module is that it is not possible to go straight to Drupal 6- I ended up creating a clean installation of Drupal 5, installing the module, downloading the XML export of Wordpress, and importing that. The upshot is that it imported perfectly. All the comments seemed to be in place, as well as posts and taxonomy. Even the URL scheme that I was moving came right over. While it does require doing some cleanup (renaming taxonomy categories for example), it was a one minute opperation one I had played around with it a bit.
After this, I created a new Drupal 6 installation and ran the upgrade script on the Drupal 5 database that contained my Wordpress data. Start to finsh took about 2 hours, most of which was spent on research as to which module to use and why. The one quirk that I ran into was likely of my own making- I set my blog entries to import as "story" types which caused some problems when I deleted the story type. A quick UPDATE node SET type = "blog" WHERE type = "story" solved the problem.
I would guess that this method would be somewhat more complicated if you were not going to a clean Drupal instllation, but for me, it worked well, and, if you're reading this, you know that it worked.