Alternate CSS Styles
Using CSS and a little server side coding, it is possible to change the view of a website with a simple mouse click. The first site I witnessed doing this was CSS Zen Garden, and from the moment I saw it I knew had to do it. From a designer's perspective this is great because it allows me to have more than one design at a time and not be confined in my creativity. From the user's standpoint this is great simply because they can choose a skin which suits their tastes.
Another reason I do this is to display first hand the unique capabilities of CSS. The ease which a website can be entirely resdesigned is mind boggling when compared to the tedious process involved in redesigning a table-based site. With those websites, every page needs to be modified, a time consuming exercise at best, a nightmare at worst. With CSS layout, everything can be changed from one file in a matter of hours.