I've got a bunch in my house, in my shop, in the bed rooms, in the basement, in my vehicles, ect. It's one of those things that I can't remember the last time I used one, but I still wouldn't want to be without it. I've also got smoke and co2 detectors in my home (which are hardwired into the house alarm system so they will alert the police/fire/EMS). I've seen a few house fires in my lifetime and it amazes me how fast they can get out of hand. The earlier they can be stopped, the better.
Speaking of fire extinguishers, I've even got a little old Halon extinguisher sitting right by my computer. Halon is a bit rough, as it's bad for people to breath and it's bad for the enviroment, but it will still put out a small electrical fire with minimum damage to sensitive elecronics; so that's why it stays there.