I presume most of 10.1.5 users have the same problem as this is part of 10.1.5 'fixed problems'. Well, I was a bit upset at having a useless Eject button, anyway ... WAS, because I just discovered that the Eject button actually works simply by pressing both the Option key and the Eject button. The 'Eject' icon appears and ... the CD is ejected! Bingo!
Note this only works for the internal CD drive. I tried it on my external FireWire burner, and CDs are not ejected with any Eject combination (but they were before I upgraded to 10.1.5). Also note this might not work for all Apple hardware, so here is my config: iMac DVSE 500 (summer 2000), 384 Mb RAM, 30 Gb, cable modem.
[Editor's note: My G4/733 with just the one internal drive still ejects properly with just the eject key, so I'm not sure if this problem is widespread or not. But if you've got a non-functional eject key, try option-eject...]

