Once in a while xfwm4 will crash, quite randomly. It seems to be when I have a few windows open (maybe 4-6) and when I click on something. After I notice the crash I right click and open a Terminal. I then type: '$ xfwm4 &; exit'. This brings up the window manager again. Not a big deal, but I thought I'd note it.
Also, sometimes it seems like everything crashes and I'm only left with my desktop wallpaper and my mouse pointer. At this point I hit Ctrl+Alt+Backspace to restart X. This is less frequent, but should also be noted.
Xfce 4.4.0, Debian GNU/Linux Sid, Kernel 188.8.131.52.
Try 4.4.1 first,. If the crash still happens, find a way to reproduce it, compile xfwm4 with debug support, run it in gdb an create a backtrace. Attach all this data in a new bug report in the Xfce Bugzilla.
PS. a way to reproduce in 4.4.1 is also good enough, if you're not familiar with this stuff