Well - had to be done. I needed to get my site updated from Drupal 5 to 6 in order to implement some better features and in general keep up with what I do for clients. It was also useful to go through the upgrade process on an existing site to get used to the pitfalls.
Overall it wasn't all that bad, but I did have to reimagine how I wanted to deal with some views, and recreate some of them from scratch. I haven't had time to really dig into the design, but this had to come first and setting a deadline helped move things forward faster.
I started by bringing the DB into a fresh empty one, removing all the modules and themes, and going through the update.php process. After running a couple of times I installed the D6 modules I knew I'd need and updated again. The new theme is a Zen sub-theme, so got that in, active and set. Another update. Searched out and downloaded new versions of a few more modules to round things out and switched a few others to different modules based on more recent experience.
This morning I had most of the views sorted out so started working on the basic typography and element styling (view items, tag representation, blog and portfolio styles, etc). All in all, not too bad. Added a new portfolio view, a nice little social media site block from DandyID to link to all my profiles, and added a twitter stream block as well.
Now back to work for a while. Have to come back to this and push the design further this weekend. I have a bunch of ideas down on paper and rolling around in my head - now that the foundation is set I'm more ready to jump on those after I get my other pressing duties sorted out!
Happy to share any other specifics of the upgrade process - post questions below so it's easier to share with everyone else.