Smartprojects have this warning in their product description:
It has 53 IO (including 4 HW UARTs, 14 PWMs, I2C bus) and 16 Analog Input pins.
It can mount and use most of the Arduino Shields (not the ETH actual version).
http://www.smartprj.com/catalog/index.php?main_page=product_info&cPath=1&products_id=37
Perhaps this warning should be added to the Arduino Mega product page too...