Most of us don't think about file systems very much, and then only when we run up on some sort of limitation with one we are working on. Perhaps it has been damaged from some sort of crash and is not capable of recovering itself, or at least not until we do something that verges on the mystic in concert with the operating system. (Windows chkdisk comes to mind, here.)
Ars Technica has a wonderful piece written by Jeremy Reimer that explains what file systems are, how many of them differ from one another and why we should care. It's a bit long, at 7 or 8 pages, but packed with information you really need to at least look at. In other words; it's worth the time it takes to read it.