First update for WordPress 2.5 branch has been released. WordPress 2.5.1 contains performance improvements along with critical security fixes for vulnerabilities which are not public yet. Totally, WP 2.5.1 contains over 70 bug fixes.
If you are using WordPress Automatic Upgrade Plugin, then upgrading shouldn’t be a problem. For others, (as always) I have put together an express upgrade zip, which contains only files that have been modified subsequent to WP 2.5. You may download it from here [411 KB].
Likewise, if you are only concerned about security fixes, you need to upgrade just 3 files (wp-includes/pluggable.php, wp-admin/includes/media.php, and wp-admin/media.php).
Just keep in mind that you need to be running WP 2.5 to do an express upgrade to WP 2.5.1, else you’ll need to download the whole WP 2.5.1 package for here and then perform the upgrade. More details on the upgrading are available in Codex.

wrote, on April 27th, 2008
Hmm…
Me still on Wordpress 2.3…
Everyday, I think I’ll upgrade today and as soon as I am online I get immersed so easily that i forget it…At the end of it I kick myself for another day gone without wordpress 2.5…
wrote, on April 27th, 2008
nice news
wrote, on April 28th, 2008
Hey buddy can you re-upload the rar file as my WinRar says:
wp2.5_2.5.1_express.zip: The archive is corrupt
wp2.5_2.5.1_express.zip: The archive is corrupt
please check !
wrote, on April 28th, 2008
I still had the version 2.3.3 on my blog, so I had to upgrade everything. I heard a lot of bad about the 2.5 version but I find this new updated version very nice.
wrote, on April 28th, 2008
Thank you.
wrote, on April 29th, 2008
Johnson: Sorry, unknowingly I had uploaded those files in ASCII mode. Just re-uploaded them. Thanks for the heads-up
wrote, on April 29th, 2008
Thilak, how much effort does it take to get your blog looking pristine, it is always heavy on the imagery and very eye catching.
wrote, on April 29th, 2008
On it…. I’ve got too many blogs to update. DOH! (over 40)