At my school all the light poles around campus have thick concrete bases which scratch the paint on my bike, so I prefer not to use them.
I've put a huge number of dings in my bike's paint by locking it to stuff. I don't know if the bike racks i've used are any better than poles, though.
Luckily, i didn't pay anything for my frame, since I found it on the side of the road, so I don't care if I add to the many dings it already had.