It was released earlier today and is noted to have fixed a lot of security vulnerabilities, so I those who are running WordPress blogs themselves should update soon.
Have just updated blogs hosted on spherebox. :)
Edit: You can get only the changed files in a zip which would save the time needed in uploading here.

#1 by Roy on August 7th, 2006
Using this zip file to upgrade from 2.0.3 to 2.0.4 all you have to do is upload it though FTP to the wp-admin and overwrite the existing files? Sorry if this is a dumb question. I am new to WordPress.
#2 by Sian Siew on August 7th, 2006
Here are the steps which you should follow if you’re unsure: http://codex.wordpress.org/Upgrading_WordPress#Upgrade_2.0.3_to_2.0.4
The usual way of updating WordPress installations is by downloading the latest zip file, extracting it and upload it via FTP overwriting all existing files. This can be annoying if you have a slow connection to the server or have multiple installations that require updating and so this changed-files-only zip file would reduce the time required for uploading unchanged files.
It’s probably safer if you follow the recommended way if you’re new to WordPress. :)