I believe this also, if you dont learn new things/practice exercise (something where you need to think), you will loose IQ (like in a long holiday). So in long term brain training exercises are essential.
I'm totally grooving on the linux bsd games like galaxies and keen that I've recently discovered. At first there was this "high" from trying to figure out the new patterns. Now even the more difficult stuff is becoming systematic (although still absorbing).