It's still not that common with probably less than a dozen countries using it or trialling it for TV.
It is the recommended format for DVB-T H.264 rollouts and I'm pretty certain every country that has deployed DVB-T with H.264 has also chosen AAC audio. AAC is also the chosen audio format for the DVB-T2 rollout in the UK.
webstereo: Well if they are going to be using it in the UK I guess that means Elgato will have to implement it properly in Eye TV then.
The UK is also using DVB-T2 which is also a newer standard than DVB-T that is used at present and is not compatible with any existing DVB-T hardware. The UK will be the world's first live DVB-T2 network.