I have a different opinion to many here. I don't think you necessarily should care in some scenarios, especially if your website is targeting a particular group of people or that it is going to mean a lot of work.
if you refer to:
http://visualrevenue.com/blog/2007/08/eu-and-us-javascript-disabled-index.html
(source: visualrevenue.com)
You can see that year on year more browsers than ever have Javascript enabled, contrary to the other answers' claims. It was at 96.9% in 2007.
So you lose 3% of potential viewers, so what, your advertising campaign will do a lot more damage than that!