Nowadays it seems that everyone has a web site - if only as an alternative medium to socialise and keep track of friends and/or post pictures. Certainly every self-respecting business has invested in a web presence.
When it comes to a personal web site, places like Myspace or Facebook only give you a limited number of options to customise your site; hosting your web site on your ISP's servers often limits you in varies ways, and paying for a dedicated server hosted by a company is not for everyone ($100 to $200 a month).
These pages will explain how you can run your own domain at home: from web- and mail servers to running your own name server as well.
The main reason for running everything at home is that you will have full control and it is going to cost you a lot less.