1/27/07: I've updated my fix for the link categories issue, so check out this more recent post if you are looking for help.

I've just upgraded to WordPress 2.1 and there were a few glitches that I've mostly resolved, but I thought I would make a note of things for others who might be having trouble.

• The big problem is one that appears to be somewhat widespread. There are no longer separate database tables for link categories and post categories, just a single categories table. WordPress is nice, and it is free, and it works great, so I'm not here to complain, but their justification that they were somehow changing this to take advantage of some elegant abstraction seems questionable to me at best. It broke my template, and I think it broke a lot of other people's templates, and most annoyingly, the API doesn't seem to have been modified to offer a method that only returns just the link categories, or at least I didn't have time to puzzle through and figure it out. I hacked it by looking at the range of category IDs that constitute the link categories and changing the "get links" query to filter out anything lower than the lowest link category. This only works because the post categories are a contiguous block, and the link categories are a contiguous block and as soon as I add one or the other it will probably break. There is clearly some other way to determine what is a link category, but I haven't had the time to get serious about figuring it out. Anyway, the links on the front page are now accurate, but the display is screwy because the wp_get_links() method seems to have changed as well, so bear with me... [Ed note: I have a better fix now, see this post.]
• The admin interface has some nice enhancements; more AJAX background loading so things are quicker, autosave while editing a post, plus integrated spellchecker! That all makes me very happy.
• All my plugins appear to still be functioning, so kudos to the developers.
• They changed the name of the Links tab to Blogroll, which is a weird narrowing, considering that most blogs I read link to a few blogs, but lots of other miscellaneous sites. At first I thought the functionality had changed, but it's just a renaming of the existing Links functionality.
• There's a little bit more confusion between what the "Write" tab does and what the "Manage" tab does. I'm sure I'll get it figured out.

Overall, it was a snap to upgrade, after I'd sorted out the category confusion, and it seems to be a bit faster. I would definitely recommend the new version.