Sounds like it's probably a bad optical drive. Good news is, there's a good chance you're still covered by the initial 1 year warranty, so can get it fixed on Apple's dime. Take it to a nearby Apple Store if possible, otherwise you'll have to mail it in to an Apple repair shop, and the whole thing will likely take about a week.
Trying to rip some Iron Maiden CDs into iTunes (so I can burn them as mp3 onto a blank CD for my car; cuts down on number of discs I need to put in car, reduces disc changing). Load CD into slot drive, CD won't read. Only occurred with some discs; others in collection worked fine. 2009 MBP 13"; 2.26 GHz INtel Core duo, 4 GB RAM; Snow Leopard 10.6.3.
Loaded problem CDs into 6-year old eMac upstairs in office (1.25 GHz PowerPC, 1 GB RAM; Leopard; tray drive): worked fine. Used home network to share files from eMac into laptop, so still got the music, but this is really odd behaviour.