In reality, those that have automatic updates turned on have been receiving a new version over the past two days that not only contains significant performance improvements but also fixes for LOTS of other issues .... as well as providing support for Ubuntu 8.04 LTS Desktop Edition, SLES 11,Windows 7 support and Red Hat Enterprise Linux 5.3.
The update is not a security update. Those running version 17 are up-to-date on security issues.
Generally, SE Version 6 supports Solaris SPARC, Solaris x86, Sun Java Desktop System, Red Hat Linux, SUSE Linux, Windows 7, Vista, Windows XP, Windows 2003, Windows 2000.
Users of Firefox 3.6 must be running at least Java SE Version 6 Update 10.
If all of this sounds a bit confusing, you can find this latest version of Java here.
Most Windows users will probably want to uninstall their current version (from the Control Panel) before installing this version. (This avoids the ongoing problem of having two versions of Java on the same computer).
Release notes for Java SE Version 6 Update 18 can be found here.
updated Jan 17,2010 10 AM ET