According to EarthTalk, a column put out by E! The Environmental Magazine, CD and DVD cases, if thrown in regular recycling, can contaminate a whole batch and ruin the other recyclables if melted down.
Still wanting to recycle them rather than throw them out?
There is an alternative:

Send CD and DVD plastic cases to GreenDisk.
The company offers individual packits that allow you to recycle small amounts of electronic waste including CD and DVD jewel cases, the CDs and DVDs themselves (which can release pollutants into water supplies if thrown away) and even computer trash, such as drives, disks and other components.