Hi,
I'm still at the beginning with Arduinos - therefore I read tutorials and howtos religiously. 
Due to more Arduino generations several tutorials and images start to divert and don't match any longer to each other - for example: The
still shows an Arduino without the test LED onboard. The test LED on more recent NG-boards is obviously connected to pin 13 either and blinks accordingly.
Not that I don't like having two blinking LEDs, but it's confusing because the images of the board don't match the Arduino NG board in this detail.
In Tod Kurt's really nice series of "spooky projects" on the other hand an Arduino NG IS pictured.
But: He puts a resistor in front of a LED - the tutorial mentioned above says " We have added a 1K resistor to pin 13, what allows the immediate connection of a LED between that pin and ground."
Does that - for example - mean that ONLY pin 13 already has a resistor and the other pins doesn't? If so - why is Tod adding one to this pin? Or does it mean that only older boards does have the resistor and the NG board doesn't?
It's nothing really critical, but I think it's confusing to beginners.