Art Paintings

Which are the customs rules for paintings and works of art at the entrance in the US?

I'm European and I intend to travel in the US soon and I bought a few paintings and works of art (nothing famous) to take with me as gifts. Is there anything I should be careful about at customs?

First, you need to list all goods other than your personal effects that you are bringing into the U.S., along with their price or value stated in USD (so you probably have to be able to covert fron the Euro) -if you don't know the price/value, say so on the form.
There is a 100 USD gift exemption, but I don't know what the assessment would be for amounts above that.
When you arrive, make sure you go onto the non-residents line! As far as dealing with the agents I'm usually quiet, only answer direct questions and don't antagonize anyone -that seems to work everywhere.