Using Pins 13 / 0 / 1 as Digital Input to Arduino

Pins 0 and 1 can be used as inputs so long as you disconnect the device when you need to upload a sketches.

But...you have to disable the USART because it overrides the normal pin functions. The code for this is:

UCSR0B = 0;

Using pin 13 as an input is more difficult.