Go into the activity monitor, and in the energy tab make sure there is nothing that is keeping the GPU on. (Look in the Requires High Performance column.)

Just browsing the web battery life is really good, but unfortunately there are a couple apps I use all the time that use the GPU for no reason. And when this happens the battery life instantly goes from 10+ hours to three.

With Java apps you can theoretically pass them a command line parameter to prevent them from being able to use the GPU, although I haven't been successful with this yet.

Source?