Something that I used to like in ProE, when you changed model units, you got an option to either keep the model size or keep the dimensions.  Example: if you accidentally built your part in millimeters, but entered values that you thought were inches, the "Same Dimensions" option would save you from having to re-enter all the values.

This is similar to Ethan Dutton's "Scale model and keep dimensions" idea. 

Such a feature would be useful in the contexts of sketch, part, and assembly.