They are great pieces of hardware, and prices are going down all the time.
CDs are great for keeping static data.
Your favorite downloads contained on piles of floppies can now be transferred to one CD, lowering your risk of losing the data. With your own CD writer, you can make custom CDs of your favorite Linux distribution, crafted for your needs. You can also make CD archives of your favorite FTP site and pass it along to friends to avoid bandwidth problems. The first, mkisofs, is required to make an image of the files you wish to burn. Most major distributions come with this utility, but in any case, getting the latest version would be wise.