I just went through the first round of updating the Drupal installation on weblogs.ucalgary.ca - not as seamless as updating a Wordpress installation, but perhaps I'm a bit spoiled there...
If I hadn't been using any non-stock modules or themes, it may have been a trivial update, but I had to tweak a whole bunch of MySQL tables used by modules (and re-install many of the modules themselves) in order to get things working.
Things still aren't running 100%, but it's close. I still need to figure out why the buddylist.module refuses to list the actual buddies, even though it can list the buddy's posts...
While digging through the list of modules and themes that were updated for Drupal 4.6, I came across the Leaf theme - very nice. Kubrick-esque, but a bit cleaner for the amount of sidebar blocks that are being used in Drupal. I'm using it as the default theme for now (partially because it's so much cleaner looking than SpreadFirefox - and being overly complex was the biggest single source of feedback I've received - and partially because SpreadFirefox still has issues with CSS clear declarations, and I don't have time to go in and debug the theme at the moment).