Javascript is a really bad idea. It raises all sorts of usability and security concerns, and still many web developers use it. It constitutes mobile code, or live data. It is often used to perform client-side validation (and avoid server-side validation). It is often used to take control of the user's browser away from the user. And it is often used to replace perfectly functional HTML for no good reason.
Evil example: evil_js.html
Note: make sure that all of your work is saved before you follow the
above link. While not all systems or browsers will crash at the above
page, many will, so be careful.
Do I think the principle of having an extendible system to enhance the display of information is a bad thing? Not really, so long as (1) it is entirely optional, and (2) the language is not Turing-complete, and (3) the user is allowed to access, modify, and prohibit *any* action.
One of the really annoying sites is ShareBuilder. They've demonstrated utter cluelessness by taking a working site, and making sure that it doesn't work unless you have javascript installed. They considered this to be some sort of improvement, even though it is an action that demonstrates incompetence. Note: I was informed that this is no longer true, but my own tests show that javascript is still required.
Home Depot solicits opinions of their customers via www.homedepotopinion.com -- which requires Javascript to be enabled to take the survey, and which further requires Javascript to be enabled to provide feedback.