LED powered by Silicon Solar Cell in overcast sky

I was amazed that a small solar cell assembly sold by Sparkfun.com was able to lightup a standard red 1.8v LED under only an overcast sky.
Also noteable was the fact that i did not need a series resistor as the inherent resistance of usually 8 ohms combined with the post resistance allowed 5-15 mA to flow no problem.
This was just a proof of concept and not really usefull in itself, but i should be able to power ano embedded controller like the propeller or xmos G4 using only a panel or two.