Downstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=717912 user had their userdirs set all to ~/tmp/ and 20k image files in there. :( Still, there was a noticable increase in memory usage on each right click. I can ask them to run valgrind or the like... whats the preferred data/command to try and track this down?
I had a similar problem recently in Xubuntu 11.10, thunar didn't respond and right clicking the desktop didn't show the menu. In my case there were few images in the userdir picture folder but they were very big. Thanks to a helpfull member of the ubuntu comunity i had solved the problem by moving those images to a different folder. More info here http://ubuntuforums.org/showthread.php?t=1798830&page=2
Created attachment 5216 Speed up template sub-menu loading code This looks related to https://bugzilla.xfce.org/show_bug.cgi?id=10138 so that patch will improve things. Since it was pushed to master, this patch builds on that one (http://git.xfce.org/xfce/xfdesktop/commit/?id=11b1396b120e4719abf19ae37589a73f900b3ff7) by making xfdesktop a little smarter when dealing with a template directory with a large number of files. There were a couple memory leaks that are cleaned up between both patches.
Pushed to master: http://git.xfce.org/xfce/xfdesktop/commit/?id=4e5cd1813862800c5d768d5ef59279b37adbdfc1
As a fix has been pushed, closing bug report.