Ask HN: Android GPU

So, I've been doing a lot of researching on the internet... actually its been two hours so far because I'm a perfectionist, anyways I'm getting a new phone and I was reading a lot about Android phones having GPUs but Android doesn't use it at all. Then I read that you can use the GPU in applications but it's just not used for the UI. Can anyone clarify this? When is the GPU used in Android, if at all. I'm mostly wondering about Android 2.3 and 3.1, since those are the latest versions.