At Mere Orthodoxy, "Why Didn't Jesus Start a Megachurch?" Megachurches are defined as a congregation with weekly attendance over 2000. They weren't seen before the 1950s, and didn't really come into their own until the 1980s. [Pictured at right: the Crystal Cathedral in Orange County, California, which seats 2900.] The linked post provides a very interesting summary, but the author seems to miss a basic point: megachurches can only flourish as part of an organizationally weak movement like post-denominational Evangelicalism. There are no Mormon megachurches and there never will be, because, in the efficiently managed LDS Church, when demographics or (strange thought this) the popularity of a bishop cause the size of an LDS congregation to swell, the local stake president will split the congregation into two congregations or make some other boundary adjustment for the local units.
The big questions — and one which rarely gets posed — is whether Evangelical megachurches are a Good Thing or a Bad Thing? My LDS experience leads me to conclude that keeping congregations at no more than a few hundred people attending on a given Sunday keeps the basic organization unit of worship and activity at a manageable human scale. I think megachurches feed primarily the egos and personal incomes of megapastors rather than the needs of congregants. Caveat: that's an institutional observation on the system, not on individual pastors, many of whom are sincere and caring.
On the other hand, megachurches are obviously doing something right in terms of meeting the perceived needs of the millions who attend one every week. I wonder if there are links to megatestimonies that might shed some light on this questions from the perspective of a megacongregant, personal narratives of the form, "I love my megachurch because ..." or possibly "I'm sure Jesus loves my megachurch because ...".