My focus in this regard is on 2.0/Beta sites. After the initial "honeymoon" period, there are often users who hang around, read questions, maybe answer a few now and again, but once the site is "seeded" with initial questions, they cease to ask any more.
Is there any way to entice these users to ask more questions?
The questions per day is an important statistic, particularly for Beta sites, so in order for a site to succeed, there must be activity. Some veteran users are uncomfortable asking questions just for the sake of doing so, and, even with the UI now actively encouraging the already acceptable practice of asking and answering, this still proves difficult in some cases.
Perhaps one could argue that the sites are just not popular enough, but I think that there is still some factor that needs to be addressed to encourage more questions. I think this is beyond the offer a badge phase, but I'm certainly not against that. What is the factor X that these users need?