Just finished upgrading to WordPress 2.3. Went off without a hitch -- even converted my categories to tags. I did have one issue with that, though. For some reason, certain posts were marked "Uncategorized" while other retained only my default "Miscellany" category. I couldn't detect the pattern. I had to "hand" edit the database to finish cleaning that up.
Other issues so far: I'm getting blank pages after form submissions in the admin interface (UPDATE: caused by having no categories 😕 ). Also, I notice that the Blogroll > Import Links panel uses the wrong taxonomy category to obtain the list of blogroll categories.