VC Fred Wilson tried out a bunch of programs that would change settings on his Android phone automatically based on where he was (like turning off wifi when he left his house) and settled on Locale.
But I'm really taken with Locale and it is the solution I opted for in the end. It's not a battery saver app, it's a location configuration app. And I think it is a very smart idea. With Locale you can tune your phone to do different things in different places.
A VC blog, April 26, 2011