I successfully upgraded 3 of my blogs which are running the 2.2 WordPress installation into WordPress 2.3. The upgrade process took a bit longer than usual since my ISP at home was slow as always. I’ve checked out all my installed plugins and everything is working out fine. I also sent an email to TLA before installing WP 2.3 to check whether their plugin would work with 2.3 and they immediately replied with an affirmative.
Since the WordPress 2.3 is a major update, I would advice you to back up your database and WordPress installation in case somethine goes wrong. And since WordPress 2.3 is introducing the Tag facility, make sure that you deactivate all the following plugins (if you are not fond of deactivating your plugins during upgrade), simple tags, Ultimate Tag Warrior and all the other tagging plugins as those plugins would definitely cause some error to appear like this one:
WordPress database error: [Table ‘aczafra_wordpress.wp_post2cat’ doesn’t exist]
SELECT cat_ID AS ID, MAX(post_modified) AS last_mod FROM `wp_posts` p LEFT JOIN `wp_post2cat` pc ON p.ID = pc.post_id LEFT JOIN `wp_categories` c ON pc.category_id = c.cat_ID WHERE post_status = 'publish' GROUP BY cat_ID
One difference I noticed with WP2.3 (but I’m not sure if this has been introduced in the previous version before WP2.3 since I skipped some upgrades) is the Advance Toolbar. This toolbar includes toggle buttongs for paragraph formating commands.