Just a point, the Solder Time 2 watch contains no resistors. And contains thsi comment. Note that it is being driven by a shift register, not the MCU.
"IMPORTANT: While hacking the ST2 it is “safer” to only make changes to the values in the LEDMAT array rather than addressing the matrix directly. The LED matrix is driven directly from the ATmega and the 74HC154 without any current limiting resistors. Each pixel in the matrix is only lit for a short amount of time, so driving a LED with too much current is not a problem. But, if your hacking leads to a program “crash” and a LED gets stuck on, it could burn out"http://spikenzielabs.com/SpikenzieLabs/SolderTime_2.html