It definitely looks interesting.
How are the headers connected to the pads? Are there traces to the nearest pads, or do you have to bridge to vias or something? Also, what about the bottom side? I think dual-sided could be very useful, provided there were vias or something to the other side available.
I also think if this were sold as a "kit" so to speak - perhaps with a button and a pin-13 led/resistor (and the headers - make them stackable, too - just like other shields) - it could serve not only as a prototyping PCB shield, but a "get your feet wet" SMD tutorial shield as well...
I would be really interested in a kit like that.
