Hey, I found a tiny bug when using the graphical expand & collapse buttons. At one point in the code, it looks for the graphics to be under "collapsing-categories" instead of "mootools-collapsing-categories". I fixed my own version, but wanted others to know how to do it until the fix is in. The error occurs on lines 374 & 376 of collapscatlist.php.
Ciao,
Maria
http://wordpress.org/extend/plugins/mootools-collapsing-categories/