It's compatible electrically, but the kind of things you connect defines which library you will need. So you can use standard servos, third party sensors, DIY sensors, and our Multiplo sensors, and there is no problem. We will release libraries which facilitate the use in some non linear, or difficult sensors.
So, with things like the rangers, you only have to write something like this:
IRRanger distanceSensor(sensorPin);
...
void loop()
{
Serial.Print(distanceSensor.getDistance());
Serial.Println(" cm");
}
There are other sensors available in the market, with this pinout, and all of them may be used with these boards, and with stardard Arduino boards.
For example, the Seeedstudio Electronic Brick line: http://www.seeedstudio.com/depot/electronic-brick-c-48.html?zenid=47b421be07a37cb9e8c74b379789dad3
Regards,
Julián