A core issue that arises as we toss our data out to the clouds is the fact that at some point we need to sync that data with our existing “traditional” on-premise systems. This fact is often lost on those deploying cloud computing tools until they attempt to drive business processes between cloud computing and on-premise resources. Then, the lack of integration becomes a huge problem.
I believe that integration is so important that I wrote a book about it way back in the Stone Age. While the focus then was on the enterprises and intra-enterprise integration, we’re now seeing integration in a new cloudy light, with new players and new approaches, but with many of the same old problems.
http://www.infoworld.com/d/cloud-computing/integration-challenges-cloud-computing-157
Although integration is the ugly side of cloud computing, integration issues can be easily addressed with some planning and good technology