Require Javascript on site?

[Vanilla]

What kind of website are you making?

Not any particular kind, I was just asking for opinions on whether it was ok to require javascript on your site as the browsers are today. Especially also considering the upcoming HTML5 and it's javascript improvements.

As i've propably already stated, many top-sites such as youtube requires javascript (and flash btw.) to be of any use, and some sites gains tremendous amounts of easier-to-use'ness(?), when javascript is enabled, facebook for example, with the auto-updates and javascript/AJAX chat.

Anyone having any consideration regarding M$ Silverlight? Considering it's cross-platform, have almost the same amounts of features, has a lot more languages available than Adobe Flash?