There's also an interesting pattern of average XP per post across the levels, with the peak coming in the middle-levels.
It would be very interesting to see whether this applies to individuals as well as the Perlmonks as a whole. By which I mean, as someone goes up the first few levels does their average XP per post increase, level off, and then decrease.
I speculate that there are two things in play here - first, in the lower levels people can get XP (or at least they used to, I confess I've not bothered reading the details for the new system cos it just doesn't matter to me that much any more) just for logging in. Second, people eventually get over XP-whoring, and are more willing to post stuff that won't get many points, or even get negative points.
Alternatively, instead of getting over XP whoring, higher level monks' propensity to submit what they know will be low-XP posts may have something to do with them previously not being able to advance any more levels. I wonder if the new system will have any effect on that. I suspect not.