The WordPress team has released WordPress 3.0.2 to users. The WordPress 3.0.2 update includes a security fix making it a mandatory update.
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.
You can download WordPress 3.0.2 from WordPress.org or use the automatic upgrade feature to upgrade it. Make sure to backup your blog before you upgrade, there are several ways to do it.