For /stats.bml, how about adding to the pretty graphs the number of times each mood has been used (I'd have thought only use the "default" moods, the ones that exist in the official clients)
I don't know how often it should be re-generated, nor do I know if it's in anyway feasible. But it'd make for a pretty picture, and you'd be able to tell if the LJ user base was made up of manic depressives, or hyperactive loonies
Just a thought, could be interesting. Might not be, though