I have experienced similar problems as bug #927 describes - which was closed due to insufficient feedback from the initial reporter. After login on slim (the display manager), xfce4 starts but xfce-mcs-manager goes into a 100% cpu loop. Eventually I can do something but everything is very slow. I have the XInput extension, and a Wacom tablet is attached. Some debugging shows an endless loop in mouse_plugin.c in function set_xinput_mouse_values. The reason is obvious, using the same variable in an outer and iner loop. Duh! This hasn't been fixed in SVN head yet. I'll attach a patch for 4.4.2 but it should apply to SVN too.
Created attachment 1575 Fixes the endless loop in the function set_xinput_mouse_values. Due to recent changes in this function, won't apply to SVN trunk.
Today I downloaded the required packages from SVN snapshot 27044 (libxfce4mcs, libxfce4util, libxfcegui4, xfce-mcs-manager, xfce-mcs-plugins), compiled and tested the code. It works in my setup (10 XInput devices), the patch has been applied by oliver and it works for me. Therefore I now set the bug to resolved.