It's not that big of a deal if one is under, say, age 25-30 or not in a high profile job. However, if you are, say, in academia where you deal with departmental politics, students, and colleagues of all sorts, the things they can find online about you may end up harming/discrediting you.
And why should I want some random person to know the names of my parents (Yahoo People Search, etc.) where they live, etc.? And what if the info these sites provide happens to be incorrect?
I have a Google counter where it reports how many people googled my name and with what keywords. I sometimes feel a bit self conscious by all the exposure.