I have Pro version 3.2.3 version. Today I was trying to edit the menu section by adding a page and dragging and dropping it in to the correct location. It was extremely sluggish and would freeze when trying to nest the menu you item into a submenu.
I did install a new Jquery Lightbox plugin, so I deactivated the plugin, then I purged all caches. Still had the same issues. So I went in and swapped the theme out for the standard default WordPress theme and that fixed the issue immediately, then I just went back in and swapped the theme back to the Pro theme and the menu issue returned, sluggish or locks up.
I can work with this for now, just thought you might want to look into this issue.