As much as it SEEMS to be a good idea to have all of these “Arduino Compatible” platforms for non-avr processors, it’s really NOT the best choice. Almost ALL Arduino shields are 5V I/O only and won’t play with the newer 3.3v cpu’s. Even worse, so many of the available shields are hardwired to pin functions based on the original Arduino UNO and Duemilanove (atmega328) pinout and won’t work with the Arduino Mega and other ‘duino lookalikes. Plus, there is this .05″ pin spacing boo-boo being perpetuated.
Still, universal ‘shield’ prototyping boards are available so there is some merit to the standard. But don’t expect to be able to plug any of your existing Arduino shields on to these new dev boards and expect to be able to make them play without some cuts, jumpers, and level converters added!