This is one of those updates that I would stress you do if your business has an online presence via WordPress. Scratch that, WordPress herself is stressing that you update to this latest version.

and I quote:

WordPress 3.0.2 is available and is a MANDATORY SECURITY UPDATE for all previous WroPress versions.

There it is, straight from the horses mouth source. here is more of the release notes:

This maintenance release fixes a moderate security issue that could allow a malicious Author-level user to gain further access to the site, addresses a handful of bugs, and provides some additional security enhancements. Big thanks to Vladimir Kolesnikov for detailed and responsible disclosure of the security issue!

Download 3.0.2 or update automatically from the Dashboard > Updates menu in your site’s admin area. You should update immediately even if you do not have untrusted users.

Sounds pretty important right? I suggest you head on over to WordPress downloads and do what you gotta do.