At the May CSS Workshop, we talked briefly about creating styles for print versions of a webpage. Then at Web Design, we talked about creating styles for handheld devices. So it was great timing that Builder.com just published a nice article on the media types that allow web developers to adapt their sites to different devices. Check out Adapt to your audience with CSS media types.
Note particularly the section toward the end entitled Support. It gives a good idea of what is practical now and what is just academic. There will be more support coming, I'm sure, so it is a good idea to get familiar with this technique.