I have upgraded to WordPress 2.5 on this blog. The process was simpler than I expected. One thing WordPress has done very well is ease the simplicity of upgrading. In this case, the lack of changes to the database schema made it even simpler upgrading 2.3.3 to 2.5 than any previous upgrade I’ve done. Summarized: remove the wp-admin and wp-includes directories, replace it w/ the wp-admin and wp-includes from the new version, copy over the updated files in the main WordPress folder, and then run the wp-admin/upgrade.php script. Done!
Of course, you’ll want to check your plugins before you upgrade. I had no trouble w/ the ones I use on this site (Akismet, MyTwitter, Contact Form 7, etc.)
One nice feature of the new version of WordPress is the built-in ability to update plugins automatically. On the new version of the WordPress Plugins screen, any plugin that needs updated will tell you and also provide a link to “upgrade automatically.” I tested it out for two plugins: I updated to the new MyTwitter 1.6 beta and the newest release of Contact Form 7.
The best change in WordPress 2.5 is the overhaul of the admin interface. It has a cleaner interface, improved post editor, better support for adding media to posts, improved tagging, and miscellaneous tweaks here and there.
If the enhanced features would improve your life and you’ve got about thirty minutes to spend upgrading it and testing out the new capabilities, I recommend giving WordPress 2.5 a try.