Javascript support has improved vastly over the last few years, though it is absolutely a consideration still. Both the better understanding of unobtrusive / DOM scripting and the advancement of AJAX has done a lot to make Javascript more important and convince "most" people to use it. You can pretty well assume that Javascript will be available in "most" cases.
Unobtrusive scripting has made great strides in acceptance on the net as well. While you will still find pages full of inline and embedded scripts on the web, most developers coding now know and will at least pay lip service to the concept of unobtrusive scripts called from external .js files. The web standards movement also deserves worlds of credit for helping convey the perception that it needs to be done this way, even if people don't always execute their sites correctly.