I've noticed that certain CD and DVDs never jam in my MacBook Pro, while others almost always wind up jammed. It also seemed that culprit discs would only jam if left in for more than a few minutes. My conclusion? Lower quality CDs and DVDs must warp slightly when heated, which causes them to jam in the player.
My solution: Turn off the MacBook Pro, and put it in a cool location for about five minutes. Then eject the CD as soon as the OS starts up. This has worked every time for me.
[robg adds: I've probably only ever had a few discs stuck in any of the Mac portables I've owned over the years, so I'm posting this as not only a hint but also a call for comments: are jammed discs somewhat common, and I've just been lucky to miss out on this problem? Or is this possibly a sign of a misaligned drive or other hardware related issue? Please share if you have additional information...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070731233449718