Lots of goodies in this release. If you're on 1.5.x and are looking to upgrade soon now is the time to help us test, as we'll get your bug fixes in very, very quickly.
Get the release at: http://docs.codehaus.org/display/GEOS/1.6.0-beta4
Blog post at: http://blog.geoserver.org/2007/10/29/geoserver-16-beta4-released/
Release notes: http://sourceforge.net/project/shownotes.php?release_id=549768&group_id=25086
thanks!