Boeing says 'immature' technology behind 787 delay

From the article: "The company has encountered numerous difficulties in bringing the plane to market due to a new engineering strategy that uses composite materials and integrates production from several international sites."

Various parts of the plane are built in different countries and then reassembled in Seattle using new materials that have never been used in a commercial airplane. IIRC, the first few didn't fit together right (don't worry, none of them were meant for customers, they're test planes) and required a lot of in-the-factory engineering to complete. One lesson could be: don't outsource your core competency. Also keep in mind that it's not just simple assembly problems, but all the other production processes that are being developed at the same time (repair manuals, tooling, software, training, etc).