I came across
this site in my internet trawling, and reading it changed a lot of my thinking about self defense. Might be worth a look, especially if you've not really thought about the topic before.
I think everyone can benefit from at least the basics of self defense. Common sense comes into play for a lot of it - knowing how to avoid situations where you'll need to defend yourself, instead of relying on a technique to escape when it's likely too late.