I am driving LEDs with a constant current driver, and wanted to increase the current ( pulsed ) to increase the brightness.
I asked my LED manufacurer what the safe pulsed current is for the particular LED, and they said 30mA - its rated at 25mA normally.
So its definately not safe to start thumping huge current pulses through the LED, ( or from the Arduio pin )
GMikes tutorial sums it up nicely, but as he says, different LEDs have different pulse tolerances, so check with the manufacturer.
Unless you have a constant current drive, include the 2c resistor.