When you go to sign up to Basecamp it displays a form where you can enter your details, but only if you have Javascript turned on. If you have Javascript turned off, then you’re presented with a message telling you to turn on Javascript.
I made my own little gist showing what can be done with the noscript tag here and it’s just a minimalist version of what the Basecamp guys have done.
Unfortunately Gist is still a little feature-bare so I had to make 3 gists for the files, even though you can put multiple files in the same gist.
index.html
noscript.css
style.css
Ironically, you’re not able to view the files above with Javascript turned off.