@48X24X48X
This looks great! I'm also working on a low-power Arduino (well, Sanguino) variant, specifically for parasitic / energy harvesting power sources (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1281416433/6)
It includes interchangeable power shields for various sources (solar/battery, piezo, peltier, RF), but nothing explicitly for charging LiIon yet.
Looks like yours is further along, though - my boards are on a monthly batch order that only went out to the PCB house yesterday.
Did you get a chance to measure the sleep current on this design?