Think about it.. When was the last time you used your drive? The only time I ever use mine is for big software packages (like Office), OS reinstalls, and the occasional person who burns a disc to give me photos, files, etc. The last one can usually be accomplished more quickly using the web, a flash drive, etc.
Even big software packages (Adobe's entire lineup) can be downloaded and activated with your license.
Don't get me wrong, I think optical drives will still be around for a while. For the average person, though, they're really not needed that much at all.
Edit: The one area I see optical media still being largely used is movies. I don't think digital movie downloads will become popular for at least a few years. Like others have said, there are some limiting factors like broadband speed and the current movie selection. It is getting better, though.