Many people have one hand on the mouse, and one on the keyboard while navigating websites. A lot of websites have handy keyboard shortcuts which allow you to interact with the website solely from the keyboard.
From Mashable:
Prepare your fingers, and throw your mouse away: you’re not going to need it. For your weekend reading, we’ve prepared a list of the most useful keyboard shortcuts for our favorite web services. So, if you need a quick reference as to which key does what on what site, this is where you find it.
The keyboard shortcuts list includes popular services like Google Reader, Netvibes and Wikipedia.