There are exceptions, though. I just bought a new Palm Centro phone, and went to use the install cd... and found that I'd left a cd in the docking station from the last time I'd used it: the install cd for my old Palm Treo 700p, from almost 2 years ago. So, there's an indication of just how often I've needed the cd-rom on this machine.
Not that I'm going to get rid of all of them. My desktop box at home has two DVD drives in it, which I'm using quite a bit to rip my DVDs. I've also needed those drives for games, either because they're huge (MS Flight Simulator was two DVDs) or because they require the disk to be in the drive to play for copy protection (really annoying). And I even wrote a DVD recently when I upgraded my home linux server, and needed a DVD drive to do the upgrade. But when you have multiple computers, you can definitely get away without having an optical drive.
On the other hand, my wife appreciates that my personal laptop, a Sony Vaio TZ, has a dvd drive, since she uses it as a portable DVD player on trips. One device is better than two in a lot of cases.