I've seen it before, and some people have said they've had luck with it. I've pretty much trained my cats to hop over the keyboard. Although on my PowerBook and MacBook Pro, they are good at hitting the numlock key at the top of the keyboard as they carefully step around the keys while insisting on placing a paw between keyboard and screen. More on the 15.4", the 12" mostly just got hopped over, come to think of it.
And I never leave a command line unattended. I had rats once upon a time, and I remember when one typed "killll" followed by something. Too close for comfort for this chica. [Look at theh placement of the k, i, and l keys. Not so unlikely. There are other dangerous key placements too.]
Funny story for World of Warcraft players: My friend has a hunter with a pet cat in the game, and he has a real cat as well. She is fascinated by the rats in Stormwind. One time he sicked his hunter's cat on a rat in-game in front of his real cat, who was pretty non-plussed.