I have experimented quite a bit with pwm dimming, and with current through the LEDs.
I generally limit the current to 18 mA, even though the LEDs I use are rated at 25mA, I find theres not much difference in brightness, and I have had less than 10 LEDs fail in the last 10,000 LEDs I have used.
I have decided to use latched TPIC6B595s to drive th LEDs, as I want them as bright as possible in full sunlight. I have designed a single sided board today, which was not as complicated as I feared.