Seems to be a common issue, but here's one "solution" if you want to risk it.
http://eatmyrandom.b log spot.com/2010/06/macbook-pro-superdrive-wont-read-any.html (you know what to do with the website address)
Oh, the thread on the Apple support forum.
Apple - Support - Discussions - Drive won't read any dvd-ejects it ...