In General I would say that the "marketing layer" of your site should be accessible without javascript.

Once a user registers and logs in to your web application I believe it is fair to require them to enable javascript in order to proceed.

However, if you don't need to create a full blown javascript web application then I recommend allowing your javascript to gracefully degrade so users can still use the site. In this case javascript best used to "enhance" the experience but shouldn't destroy the experience if it's disabled. Hope that helps.

Also, keep in mind that this also depends on the organization your working for. In the case of government websites with strict accessibility guidelines, sites need to work without javascript enabled because screen readers for the visually impaired have a hard time viewing dynamically generated content.