For quite some time I've used a pattern when it comes to configuration to hide it behind some interface. This way I can easily fake it in a unit test but typically there has been an implementation relying on a configuration file. Then when I started working with Azure a few years ago I started to check in a number of different configuration files for different environments and scenarios. But there was always a problem with configurations; while very convenient that they could be changed manually and quickly change the behaviour of my service at the same time those changes are hard to track. The solution was so obvious I didn't think about it until recently in a discussion I had with a co-worker. Configuration should be kept in code. I already started the process by checking configuration files into my source control system, but taking it another step and actually make it part of the code so that you need to recompile is for many reasons a better idea and also possible when working with cloud services.
Configuration files definitely have it's place but when it comes to cloud services, redeploying your service is fast enough so you can actually recompile and redeploy rather than changing a configuration setting. At the same time you should get a trail of changes (the change is checked in before deployed, right?) and you will run a number of tests before deploying too right? So a simple configuration change is now actually treated as a simple bug fix; it is validated before deployed!
I realize this is not a new idea, but I find it very appealing the the cloud service scenario and worth mentioning here because somebody like might have overlooked this just as I did.