I never used a surge protector before and I leave my computer running 24/7.
In the last 10 years that i've been using a PC, I've never once encountered any kind of surge that has caused any damage to anything electronic in my house. I suppose it's still a good idea to use one but from my experience, power surges are not really neccessary. At least not here where I live. I must also mention that I live in L.A. It rarely ever rains here and its even more rare to have a lighting storm which can cause electrical surges.
I, on the other hand, have experienced two or three surges with the potential to damage electronics. Any electronics of value I keep on surge suppressors. A cheap stereo though, which was not protected, was ruined once. Also, a few of cheaper suppressors burned up (small loss, considering what they're protecting).
The moral is that it can and does happen. Even if you're area doesn't seem to have problems with it, all it takes is for someone to make a mistake once.
Edit: Another habit I've gotten into is unplugging electronics when I know I'm not going to be using them for a long time. Things can't get damaged if they aren't plugged in. Of course though, it's hardly a solution for things that are used more than about once a month, or if the plugs are in hard to reach places.