Well?
Check what the Master has to say: http://www.straightdope.com/classics/a2_317b.html
I hate that sound because I associate it with the interruption of a perfectly good day dream.
what?
I don’t.
The sound of fingernails on a chalkboard, the tines of a fork on good china, styrofoam on styrofoam, etc. have no effect on me whatsoever. Well, OK… no more effect than listening to, say, Limp Bizkit… but I digress. Frankly, I’ve never comprehended the reaction some people have to these sounds.
However, in defense of the “vestigial reflex” theory, a friend of mine once claimed to have conducted an experiment. She worked at a daycare and one day she ran her nails across a blackboard to see the reaction from all of the babies. She claimed that all of the babies visibly winced and got distressed looks on their faces. Other sounds did not get the same reaction.
Thanks, CKDextHavn. Sorry.
Forget fingernails on a chalkboard…
How about the sublime whine of the dentist’s drill 
here’s what I know about this subject. I’m sure you have heard of the company BOSE. Amar Bose did studies similar to the ones that “The Master” spoke about in his answer. From what I learned the ears are trainable. They have become accustomed to every day, dull bland, normal sounds. What Bose found was that the ear is constantly being trained. Because the ability to hear is one of our primal senses, the brain gets very interested by noises that are not familiar. The ears also like sounds and tones that it isnt accustomed to and tries to learn them. Thats why Bose is the best selling speaker in the world but the least accurite speaker. People always say --“Wow that Bose sounds good”.
I was basically trying to say, if you heard the noise of fingernails running down the blackboard everyday–your ears would become accustomed to it. The first few days may be unpleasant.
Maybe if Im really near the board I can hear it. But just the thought of it makes me quiver like chewing a big mouth full of aluminum foil.