Here's a really nicely written up tutorial an how to set up a simple File Server using Ubunto Linux, and Samba.
How To Build Your Own File Server from Intac.net
This would be great for a home system or a small office that needs simple file sharing on a dime. Or perhaps even for larger organizations that need on the fly file space for temporary use. Or just to get more practice with Linux.
Of course if you are a small office using this method you should be using RAIDed drives so that if one drive goes out you can rebuild the data set by replacing it. Also, don't forget the backups.