I have had my iMac for a little over a month now. No Problems in that time.
Last night i was watching DVD movie (legal, not burned) and put the movie on pause for a while. The computer went to sleep. When I woke it up the DVD player said there was an error and it ejected the disk.
I inserted the movie again and, without an error message or anything, it made a little noise and then spit it out.
I re-booted. Same thing. I tried a variety of disks.
Over half of my DVD's will do the same thing, including my Mac OSX DVD.
A few DVD movies play fine, i checked to see if it was a dual layer issue. It doesn't seem to matter. (Also checked burned and pro DVD's, no same randomness)
The drive plays all CD's perfectly.

When i put in a disk i know it is going to spit out there are a few light clicks a whirr or two and then it ejects it!