Arduino Uno: Pullup Resistor I have been reading a bit about the internal pullup resistor. I know from past projects in school that resistor themselves are fragile (burnt one by accident due to higher current than was made for).

I have two different Arduino models. One by Intel and rest are standard Arduino Uno.

So I was wondering about safely using the internal pullup resistor on the Arduino Uno. Hence my question is about the internal pullup resistor pinmode; How many pin can you connect to it safely and not overload it?
Each pin has its own, separate, pullup resistor. 

I don't believe you can damage it by drawing current from the port, because the pullup resistor is only active when the port is in high impedance (hi-Z, input) mode. 

The pullup resistor can be damaged by overvoltage, static discharge, and the like. 

The Uno has 20 kOhm pullup resistors according to this tutorial. If you feed it a 0V signal while the Atmega is running at 5V, the current will be a quarter of a milliamp, which is miniscule.