I've found that I accidentally hit the button all the time when I have it on my lap. I was on a flight the other day and it kept hitting the arm rest, eventually, I just stopped putting the tray back in.
I wrote LockCD application after giving up on finding a properly functioning software that would lock the CD ROM eject button which i hit quite frequently on my Lenovo T520 laptop. The main problem with the software found over the internet was that it wouldn't retain the lock state after Sleep/Resume. I made it freely available at LockCD / Wiki / Home