I have it turned off in my main browser with NoScript, and then selectively turned on for sites I frequently use (like HN) with poor usability without it (like HN). It's actually surprising how many actually require it though. I prefer to use emacs-w3m, and thus not get distracted with images or anything else.

But no, JavaScript is not required to sign in (that's what HTTP Basic and Digest authentication are for), nor to post comments (that's what the HTTP POST method is for); both capabilities are available to a non-JavaScript browser.