What would go a long way in improving site participation would be simple improvements to the site itself...ie, better navigation and all the kinks finally worked out before any new features are implemented. We then might have some retention of membership thus gaining more constant participation. (I know quite a few great members who have left the site, never to return, because of these issues.)

Simple, genuine concern, such as Apo's. No flaming, spamming, or outright insulting necessary.