I see lots of JavaScript advice centered around making sure your web application still works when JavaScript is disabled.
But is that still an issue? What percentage of people do that? And are they are large enough group to actually care about?
I'm being asked to create more interactive pages by my customers (a la AJAX and JQuery for me), but interaction often comes from JavaScript. -- Yes, I can do some cool things with CSS, like :hover, but that doesn't display a div as a modal popup. :)
Take a look at the w3schools stats page.
http://www.w3schools.com/browsers/browsers_stats.asp
It helps to understand your audience though. If your users are primarily mobile phone users, the percentage of your viewers with no JS capabilities could be much higher.
EDIT: Adding an additional source to corroborate my original link:
http://www.thecounter.com/stats/2008/November/javas.php
There's not a ton of documented statistics out there. This plus the w3schools answer should give us a conservative estimate of the number of users with JS disabled. I'd guess it's a tad bit higher.
Its good form to let your application degrade gracefully to function without Javascript. Depending on the circumstances too, it may be in adversely affecting your SEO (content not accessible without Javascript etc). The same thing can be said about screen readers, which I hear can't read Javascript generated content so well.
Generally, it's not too difficult to provide this fall back for a professional site.
Also, if it's a shopping cart, do you really want to lose any potential customers?
Given that firefox extensions like NoScript and Flashblock exist and seem to be popular, I would say it is still very much a consideration when it comes to web development and may be more common than you might think.
If you use firefox try the NoScript extension,-- visit stackoverflow and disallow scripts for the stackoverflow site, you'll see they do a nice job of messaging.
But yes its important even if its not the majority case.
OK, we are now looking at 5% of browsers have JavaScript turned off. Not a very big group.
Because Javascript is always on by default, someone has to actually go out of their way to turn it off. These people should also know that when they visit a site and something isn't working properly to turn it back on. The only exception to this is mobile device users.
So, unless you've got a lot of people using a mobile device which doesn't support Javascript, the only people you'd be alienating would be those who did it to themselves and know how to solve the problem.
Seems like a non-issue to me.
ps: oh - just don't hide all your content in the Javascript: you still need search engines to find you.
Edit to respond to the comments and downvotes:
If you're building an application, as the OP is talking about, then you should be able to expect that your users can turn off their (paranoid) plugins, so that you can use whatever reasonable technologies let you get the job done. This includes Javascript and Flash. If you're building a site, then definitely build for the lowest common denominator and add progressive enhancement with Javascript and whatnot. There's a very important distinction between an application and a site.
(and yes, i realise i've altered my original argument)
Don't forget disabled persons with screen readers or text-only browsers, and search engines. If you work for the goverment or a company that contracts with the government, you are required to support that 1st group. Also, the number of people using extensions like NoScript or mobile browsers is actually rising, so you can't count on this staying that low.
Also see this question:
http://stackoverflow.com/questions/121108/how-many-people-disable-javascript#121128
For an internet user, it should be (and actually is in a rising percentage) basic common sense to use something like NoScript for Firefox to deny JavaScript (and other scripts) by default to any site. They have a Whitelist to pick the sites where they want additional functionality. Your Website should convey what it has to offer in pure HTML, so that a sensible user has something to decide that your site's additional functionality interests him enough to open script access.