The WordPress upgrade instructions are pretty good, but they left out at least one recommendation I wish I’d heard before I got started:
Take screenshots of the current version of your weblog!
Once you convert to version 1.5, you won’t be able to view your old version any more. But if you are planning on keeping the same visual design, with the very significant reorganization (and improvement) of WordPress themes, you will have to make a lot of little changes in a lot of different places. How will you know if the new version successfully replicates the visual design of the old?
The only way is with screenshots. At the very least, take one of your home page and of a single story page. But you ought to take several of the single story pages, with differing comments situations (no comments, some comments, commenting open and closed, you logged in to WordPress and not logged in, etc.). And you should take shots of your archives pages, too.
You might also want to save some of these pages as static HTML, so you can review the hidden elements, in addition to the visuals that the screenshots preserve. I wanted to do comparisons of the meta elements in the head of the document, but it was too late for that, too.
Anyway, I’m 95% done now, but I suspect the last 5% will take as long as everything up to this point!