Are you designing for multiple devices?

I ran across this article on Smashing Magazine today and as I scrolled through it I was realizing that I already do a lot of these things on new sites we launch. So now I'm curious if most other people are building sites that adapt to the display device or fixed sites in favor of other solutions.

So if you are designing/building flexible sites any tips?
If your not reasons why?

My Most project are from local people and They all want that to run o Web Browser only, None of them( No All of Them ) is actually aware about multiple devices or run there sits on Mobiles etc.

So I don't Care