An updated version of PHP 5.3 has been released - the PHP development team recently released 5.3.1 with over 100 bug fixes and improvements to the 5.3 line. Some of the fixes are security related.

Users and webmasters probably won't be seeing this in a normal hosting environment for a little while yet, but developers are using this in their development environments to test their applications for compatibility and to start taking advantage of the new features introduced in PHP 5.3

If you are interested in how you can make the move to PHP 5.3, you can read the 5.2 to 5.3 migration guide. If you really want all the details about what's changed, read the changelog.