In the The Journal for Baptist Theology and Ministry, there is an excellent article on the Emerging Church Movement by Southern Baptist missiologist of North America, Director of LifeWay Research, Twitterer, and prolific author Ed Stetzer.
"The Emergent/Emerging Church: A Missiological Perspective"
Dr. Ed Stetzer
Vol. 5. No. 2.
The Journal for Baptist Theology and Ministry
The Baptist Center of Theology & Ministry: A Research Institute of New Orleans Baptist Theological Seminary
Andrew Jones, Tall Skinny Kiwi, also recommends the article, "Dr. Stetzer has an outstanding paper on the American emerging church just released on The Journal for Baptist Theology and Ministry. Well researched and worth the read."
Stetzer does an excellent job of telling the history of the movement drawing on many good sources: Tony Jones, Scot McKnight, Brian McLaren, and Eddie Gibbs and Ryan Bolger.
He concludes by expanding on his taxonomy: Relevants, Reconstructionists, and Revisionists. He explains further that this based on a missiological assessment. I think all of this is very helpful.
Essentially, he is arguing that it is important for all churches to adapt to their culture in order to communicate with them. However, they should not accomodate to the culture too much. He tries to identify some ways that the emerging church movement is doing the former and some ways they are in danger of doing the latter.
Stetzer's work is mapping the terrain. Others who are leading churches will need to do the constructive work on what precisely this looks like. I think my paper on Rowan Williams's missional ecclesiology does some helpful work in this regard--arguing that there are four practices that cannot be lost in contextualization if the church is to remain faithful.
But if you want to get a basic idea of how to evaluate the emerging church movement and to understand its breadth, you cannot do better than reading Stetzer's analysis.