The official announcement is
here. The upgrade is mandatory if you want to keep up with security fixes. Note: it looks like this update is not just a simple drop-in-and-run-the-upgrader affair, but there are
changes to several javascript and other templates as well. If you are (mostly) using the default templates this should be quite easy to deal with by refreshing the templates in question. If you are using customized versions of these templates it looks like you need to do some manual editing to avoid comments etc. breaking on the new version.