I thought this forum was about helping people interested in using Arduinos in their different projects, not for flaming those who try to help!
It is the problem is that dhenry has some strange ideas about lighting up LEDs and throws in all sorts of irrelevant curve balls that the net result is that a beginner is confused. He says things and will not back them up, or talks about fourth and fifth order effects of something as if it was a first order effect. For example he is always banging on about the 40R output impedance of an arduino pin and ignoring the fact that this is only for small currents and I have measured pulses up to 250mA from a pin which puts the impedance down to at the most 20R. Anyway I think the result is that he has scared away another newcomer in a effort to make himself look smarter than he is. It is a shame.
It is always been my belief that electronics can be simple. The trick is to simply things as much as possible but not to such an extent as to be wrong. That is what I try to do, I don't always succeed.
On this topic I normally say:-
With an LED you always need something to limit the current, the simplest of which is a resistor.
Now that is not like saying:-
You always need a resistor.
But it avoids all the complication of mentioning constant current supplies and the rest when all the beginner needs to be told is that you can't just stick an LED across a digital output.
Thanks for the comments on my links. 