To each their own but I've never bought one and have never used one either and I'm happy with my position.
I've always maintained that it is more of a protection against chemical sprays rather than impact protection. But I do understand the argument from the other side. Should there be an impact not enough to shatter a filter but enough to scratch a front element then filters might offer some protection.
Now whether a scratched front element does much to degrade IQ is another story. I seem to remember a lensrental blog entry on just that.
But a scratched front element does degrade the resale value though.