Well, the forums run by the company I work for are even more of a "ghost town" than this one. So maybe the traditional forum is going the way of the Dodo (Raphus cucullatus), as Steve R Jones says. I would also corroborate Steve's other observation, that "they are only as good as the members make them".
To go on at length ... as for participation from the community, we discussed some of our detractors/distractors a little in this old thread, we have competition from other sites, including some dedicated to PHP and some dedicated to programming in general (StackExchange's "schtick" on this seems to have convinced quite a few people [and search engines] that they are the bees' knees), and then there's the whole question of whether or not PHP is a dying language.
Finally, speaking of dying, I'm of the opinion that this community and F/OSS in particular suffered bigtime when Tim Perdue died, even though he was no longer associated with PHPBuilder directly.