But, myself, I browse with NoScript turned on at all times, and if I come to your site and it does not work because JS is required, then I will simply leave and go to the guy next door who does not require JS just to use his site.
Take the high end of the Yahoo! estimate from this thread -- 2% of your users have JS turned off. If it takes 10% more programming time to support those users, is it worth it? That's a question that can only be answered in a specific context.
You are "supposed" to build your app using progressive enhancement and graceful degradation. But that puts an additional burden on the programmer. If that burden is worth it to you, then do it. Otherwise, don't bother supporting JS-disabled users.
My startup is focused on b2b users. Few of them don't have JS. It takes more of my mindshare and time to support those people. Without an affirmative business case to support those people, I cannot justify it to my cofounders.