I can’t find the damn changelog for this release, if anybody has an idea where it is, please drop a comment.
For those you who can’t find a binary package for your own distro (or *nix-like OS), but have neither time nor patience to compile Xfce from sources, you should check out the graphical installers from the guys at os-cillation.com. They work great! I know, I use them myself :).
Update: Xfce 184.108.40.206 has been released quickly after 4.2.1. It includes a fix for a bad bug where panel loses its configuration when saving the session in 4.2.1. Found the changelog for 4.2.1 here.