I'm a little leary with Sparkfun because one of their first tutorials for blinking LEDs doesn't connecting resistors. You can read in the comments that several people have mentioned it is wrong multiple times, but it has not been updated. Could have shorted the MCU on the first project, no less. And a beginner, such as myself, wouldn't have even thought about it.

From one of the comments:

The author fails to mention Resistors! I wonder how many have smoked their MCU (they can only handle 20mA/pin).

Others have brought it up, but no one has changed the instructions. A beginner would have no idea this is needed.

[www.sparkfun.com]

Now I admit I could be wrong and no resistors are required.. as I am a beginner, but every other introductory tutorial for LEDs mention the resistors. But please correct me if I'm wrong? Because even Sparkfun mentions:

Limiting current into an LED is very important. An LED behaves very differently to a resistor in circuit. Resistors behave linearly according to Ohm's law: V = IR. For example, increase the voltage across a resistor, the current will increase proportionally, as long as the resistor's value stays the same. Simple enough. LEDs do not behave in this way. They behave as a diode with a characteristic I-V curve that is different than a resistor.