Exhausts PHP memory limit on big sites

The way you are loading each node in is creating a huge static array of cached node objects. This eventually gets full and kills the module from processing any further.

You need to change your node_load() so that it resets the internal function cache on every call. Use:
$node = node_load($val['nid'], NULL, TRUE);

I noticed this in 5.x version, but your code hasn't changed in the 6.x version from checking CVS.

Hope it helps.