So on this note...
Power LED Shield V2 is on its way. It's a total redesign, using a higher capacity driver module by Recom Power (RCD-24).
Comparison of major features between V1 and V2: (V1 / V2)
Max input voltage: 24 / 36
Max output voltage: 22 / 33
Max output current: 1000mA / 1200mA
Max LEDs in series per channel: 6 / 10
Channels assignable to PWM pins: 3,9,10,11 / 3,5,6,9,10,11
Dimming method: trimpot + PWM / trimpot + PWM to analog conversion
Plus I fixed a few bugs and annoyances.
I'm especially happy with the PWM to analog conversion for dimming. One of the big problems I have with PWM is using it to dim things like a bicycle headlight. When you're moving, the PWM makes for a psychedelic experience - and it's sort of dangerous. Also, analog dimming increases the efficacy of the LEDs because they produce more light per watt at lower currents.
One last feature I'm still working on is a logarithmic (or exponential) dimming curve. The human eye senses light on a non-linear curve. What looks twice as bright is actually about 10x as bright. And what looks half as bright is actually 1/10 as bright. I think the shield will be much more useful with this feature.