With OS X Mavericks, users are able to use Activity Monitor to view which apps are using the High Perf GPU, therefore, sucking more power from the battery. This is exposed by the 'Requires High Perf GPU' column in the Energy section.
I find this very useful and often close those apps if I am not using them.
I've also found that sometimes apps start as not requiring the GPU, and later switch it on during their lifetime. For example, I've noticed this with Sublime Text 3 and some others.
I was wondering - is it possible to get a notification when some app switches to the High Perf GPU?