It depends on your audience and type of website.
For instance, a graphic artist portfolio will not be visited by blind people or people using text browsers. So in that case it's not so important to build nice degradable JS, expecially because it will most probably be used for graphic effects.
If, on the other hand you're developing a news website and you decide (for whatever reason) to dynamically load your news with JS then you should definitely make it degradable. Also, remember that the spiders of indexing engines may have difficulties in indexing content loaded with JS in your page.
At the end of the day, in most cases it's not so difficult to program the site so that it works without JS. If you're retrieving content dynamically you already have the server-side code to load the content, you just need to accomodate how the page is called.
Same thing for forms, you can send the content via AJAX or via a normal POST, the backend will be pretty much the same, so it's again easy to implement.
Of course, the problem is not even posed for JS code that is purely graphical.
