The second revision took form and arrived in me mail a while ago. Apart from going back from the boost LED driver to the filtered PWM MOSFET approach, I'm also adding two more LEDs and a heatsink on the back. The Atmega 168 has 6 PWM channels and at least 6 ADCs, so there is no reason not to! Each one of these LEDs are tested to about 150 lumen at 350mA, so that is going to be 900 lumen in total.
On the board above you can see the PWM RC filters on the left and the MOSFETs with the sense resistors on the right. The RC filters will make the PWM signal into a smooth analog signal to control the MOSFETs, but more on that later.