Well, I have successfully upgraded this site to Drupal 7, following the instructions in the UPGRADE.txt file provided in the Drupal tar file. However, I have not upgraded the theme. I'm going to retheme this guy later. For now, I've enabled the new Bartik theme that comes in Drupal 7 core. If you've been to drupal.org lately, you'll recognize it.
The only contributed module I retained is Mollom. Upgrading Mollom did not retain my settings: I had to set up Mollom almost from scratch again. But that wasn't hard.
In any case, I look forward to sharing my Drupal 7 discoveries with you in the coming weeks.