I don't use Twitter except when I'm linked to it and for occasional searches, and it's been a huge step backwards with the new UI that was forced on everyone a few months ago. It even has a loading screen because it's much slower, and somehow also manages to show less content than the previous design.

If I remember correctly there was a brief period a while ago when they did use a JS-only "web app", but then switched back to simple HTML with JS enhancements (and I seem to remember they announced that change with much pride).

Of course, there is always mobile.twitter.com that is still static-only and quite usable without JS, but IMHO Twitter is the perfect example of how the "modern web" is doing less with more.