I'm personally of the same opinion as Stephan. Adding functionality via JS is fine, but at least make sure the core system works without. If someone wishes to browse either with it without it enabled, they should be able to view the content and use the site regardless, in some way or form. Take this braindead site as an example:
Give me one good reason why they do the redirect for non JS enabled browsers. It's a search on the landing page. Just about the simplest thing you can expect to do on an interactive page, yet they refuse point blank to allow non-JS clients. Why?
As to why browse with JS disabled... Try using an old machine and browsing the web sometime. It's really amusing to have a machine practically stall on you because of all of the superfluous and totally unnecessary effects and other JS gubbins which one likely has no interest in. What about malicious JS code on hacked pages/sites? Plenty of reasons to browse without JS generally, IMHO.
If JS is available, then by all means use the extra functionality. But please, just don't penalise those who browse without. There's neither reason nor excuse for doing so, other than saving oneself some minimal extra effort.