Looks like upgrading to WordPress 2.6 from 2.5.1 is really easy. Delete a wp-admin and wp-includes directories, save your old wp-config.php file, upload new files, copy values from old wp-config.php file into new file, go to admin screen to do a quick database upgrade, and wha-la, you’re done! Hopefully everyone has had the same experience I’ve had, and no one has had to completely reinstall WordPress like I had to awhile back (what a pain!). Here’s some instructions on upgrading to WordPress 2.6 in case you can’t find it:
And here’s a little about new features and whatnot in WordPress 2.6
See this video and more here.