As Gandalf3 recently pointed out, Campbell has recently added code that allows for saving images externally. This sounds like the feature which experimental branches of Bake-Cycles were using to save baked images automatically when a bake finished.
I can't find it exposed in the UI so I assume for now it's hidden until this is all sorted out.
This would be very useful for batch baking in scenes that already have dozens or more textures since finding everything that has just been baked can be difficult.
Does anyone have some script ideas on a simple way to access this new feature so that all images are checked for changes and saved if changes have been made?