How about total attendance count for all conferences between Python/Ruby/Perl. If Perl was still kicking ass on that (it has historically had some of the best conferences) I'd be surprised.
That's probably a good measure. YAPC::NA this year was the biggest ever, I seem to recall hearing (and I definitely remember there were more women there this year than ever before...it was commented on during the closing address as being a great milestone for the Perl community). But, YAPC is still a pretty small conference, by design, and there are multiple YAPCs each year, in places all over the world, with the goal being to be friendly to independent volunteer hackers rather than huge corporations.
