If the speed and simplicity of paper prototyping are not enough to convince you to step away from the keyboard, then consider two other options for rapid prototyping:
Balsamiq Mockups (http://www.balsamiq.com/)
Axure RP (http://www.axure.com/)
I personally recommend Balsamiq Mockups. The prototypes it produces have a uniform but hand-drawn look. This will accomplish the same thing as paper prototyping but with more consistent output and easier collaboration across distributed teams. Both of these tools can produce fully interactive mockups, as well as allow the user to actually click through the prototype. Ultimately, paper prototyping is still faster and anyone can contribute.