my 2007 imac 24" desktop has started to have the same problem ejecting discs - i can hear the whirring, then the disc remounts and is recognized. went thru this with two discs, thinking that perhaps the disc was the problem. tried the entire list of disc ejecting procedures listed in apple support several times and eventually ejected both discs. finally decided to not use the drive.
after reading the very well written and photographed descriptions of the methodology for replacing an optical drive, i've decided to buy an external drive and use it for the not-so-frequent occasions when i need to use a disc. (i'm not very tech savvy, altho i'm handy and might be able to manage the process, but it looks difficult and time consuming, and risky for someone who doesn't have experience with computer innards.) i've found, after some searching, a top loading drive (lite-on, sold on amazon) which i plan to buy, since the problem with the drives seems to be the mechanical eject mechanism, and a top loader will eliminate that problem.
this is a great site, and so many of the contributors have such impressive knowledge. thank you.