Granted this person is a designer and this information posted on his blog is logo related but it relates to the entire creative community.
This post is a must read for all artists and their intellectual property - jonengle.com/2009/04/accused/.
This also makes a great argument for tagging everything with meta data and tracking your work.
**UPDATE: Thanks to Jason Campbell who sent this link to some info about the other side of the story, read it here.