They say: "The Open Clipart Library (OCAL) is the Largest Collaboration Community that creates, shares and remixes clipart. All clipart is released to the public domain and may be used in any project for free and with no restrictions."
I say: wow! thank you so much for providing such an amazing resource and it's a fantastic example of generosity and collaboration on our open worldwide web. Go there, use stuff - and also consider making stuff for the site.
And you can follow on Twitter: https://twitter.com/openclipart