WordPress 3.0.3 has just been released.
It is a security release which fixes issues in WordPress’ XML-RPC remote publishing protocol. If you are using XML-RPC and your blog has untrusted Author or Contributor users, then you should upgrade as soon as possible.
The release consists of 4 modified files, so it should be quite straightforward to update your WordPress website(s).
This is the second WordPess security release in recent weeks, with WordPress 3.0.2 being released on November 30th.