@jcl - no, I'll be driving 96 leds (4 groups of 24 at 10ma a piece) via PWM through various sequencing & fading patterns. Although they could potentially be on all at the same time the average will be much less, but still considerably more than the Mega.
@dogsop - interesting - I was banking on the 1.2v / cell and assumed that would not be high enough to run through a 5v reg...