Hmmmm! I wonder if it could be because of how I installed mogile? (Namely, I don't know how I managed to install mogile *G*)

Okay, what does

perl -MMogileFS::Server -e 'print $MogileFS::Server::VERSION . "\n"';

say? Thought that might not be much help; I'm not sure whether mogilefs might not have be looking in different paths for included modules, but worth a try.