A friend has lent me the book "emergingchurch.intro" by Michael Moynagh. I haven't got far with it yet, but there are already comments that I want to make about it!
Firstly, doubtless traditional churches do need to learn things. They need to make sure that it is only the message of the gospel that people object to: they are not put off by - for example - not being able to understand what we are saying; feeling self-conscious about singing in public; and so on.
However, Moynagh faces the issue of postmodernism at best with ambivalence, when from a Christian point of view, postmodernism needs to be rejected. Moynagh seems to argue that since we live in a postmodern society, we need a gospel that is postmodern-friendly - that accepts the fact that truth is relative and personal, and so on. But postmodernism isn't even able to properly support itself! - is the statement "all truth is relative" objectively or subjectively true? It clashes with what the Bible says about God and truth - that God is really there, and that his revelation is absolutely true - in a sense more true than anything in our own experience. The elevation of subjective truth over what the Bible asserts is objectively revealed truth is incompatible with what the Bible says - in Bible terms, it is effectively idolatry - the subject creates and worships a god in and of their own imagination.
Also, the concern expressed for churches to "fit in" culturally (by having coffee-shop churches etc.) misses the point that the gospel is by definition culturally unacceptable. In 1 Corinthians, Paul acknowledges that the gospel - and specifically how it is presented - is regarded as foolishness to Greeks, and offensive to Jews. But that didn't mean that his style of presentation changed. In fact, in a sense, the whole message of the gospel runs counter to the culture. The salvation that God offers in the gospel isn't "credible", it is outrageous; to imply that the gospel is somehow "cool" is to offer something that is not the gospel.
Finally, the whole idea of people finding a church that suits them - of churches offering a variety of styles of worship, for example, for people to pick one that they are happy with - misses what the New Testament teaches about the nature of church. Churches are environments in which there are no divisions - male/female, Jew/Greek, slave/free, presumably young/old. All are redeemed on the same basis; all are given gifts for the edification of the whole body; all uphold one another. If people go to a "church" that only has people that are like them in it, they are not going to a New Testament church.
This book may not be a formal statement of the theology of Emerging Church. I don't know enough about it yet to know. I promise to keep learning. But if it is, there is cause for concern!