John Piper has recently spoken out against IM. Cody Lorance (don't know who this person is at all) responded. Our brother Warrick Farah over at the fine blog Circumpolar has summarized the two issues and offers his own two cents.
I personally find the whole incredibly annoying. Not because the discussion is not worth having, but because the people engaged in this discussion simply do not have, imho, the civilization resources to make a positive contribution to the discussion. Here is what I said in a comment at Circumpolar:
In the end I suspect that American evangelicals are just not really capable of having this conversation. As Americans we are a history-less and rootless people. As evangelicals we have, for the most part, tried to get by on the bible alone (a ridiculous project) while getting rid of tradition and ritual. A tradition that lacks an appreciation for its own rituals, history, and traditions simply is not capable of making a useful contribution to matters of religious identity for Muslims [or Christians] who are deeply invested in history, ritual, and tradition.
One attempt to define IM is here. It is the best one I've found so far.
Insider movements can be defined as movements to obedient faith in Christ that remain integrated with or inside their natural community. In any insider movement there are two distinct elements:
1. The gospel takes root within pre-existing communities or social networks, which become the main expression of “church” in that context. Believers are not gathered from diverse social networks to create a “church.” New parallel social structures are not invented or introduced.
--Rebecca Lewis, 'Insider Movements: Honoring God-given Identity and Community, p 16, IJFM 26:1, Spring 2009. (Google it...)2. Believers retain their identity as members of their socio-religious community while living under the Lordship of Jesus Christ and the authority of the Bible
(Update from 8/2013: I have written a substantial article on this topic. Check it out here, here or here.)