Reporting from the Innovation3 Gathering in Dallas, Texas -- I just finished giving a presentation that breaks down the members of every megachurch. "There are only 3 people in your church," I told them.
The best and most recent information on megachurches available was collected by Warren Bird (Leadership Network) and Scott Thumma (Hartford Seminary). They invited me and a small group of other scholars to look through their data. Here's a small sample.
I used focus group transcripts to look at the process of joining a megachurch. I call it "The Three People in Your Church":
The powerpoint is presented here as a "movie". Enjoy!
Also, you can read more on megachurches here.