I was able to sit in John McKay's presentation at the Arts and Cultural Convention, " Fundamentals of Copyright, Trademark, and Intellectual Property Rights." He spoke eliquently on many facets of U.S. copywright law as it relates to artists, which I'm very clearly not qualified to pass on, however I ran across a number of articles the next day which carry on his points.
Cornell Information Center has a wealth of information on the nuts and bolts of the copyright law and ways your work is and is not covered.
The Blog Photo Attorney has an illuminating discussion about the legality of the use of the photograph that the now famous illustration of Obama was based upon.
TechDirt continues the discussion with "Yes, Artists Build On The Works Of Others... So Why Is It Sometimes Infringement?"
Finally, the Wall Street Journal has the definitive word in the comprehensive article on art and copyright: "Color the Law in this Area Gray".