Am I insane or are cache-control headers unreliable? I always set cache-control: no-cache on my S3 files but still get complaints about people getting old versions with broken pages as result.
Some CDNs don't always listen to those (I've noticed cloudflare especially has a problem with them if I don't add the files to the ignore list in their control panel), maybe that's it?
It's not a hack at all for resources you control - in fact, it's encouraged to do so in order to use very long lived Expires headers while still being able to deploy new versions of your app.
It doesn't work for unversioned library code though where you want to automatically upgrade all users of your code as is the case with Twitter it looks like.
Problem with these is that many caching proxies consider all resources with a query string to be dynamically generated and won't cache them at all, which in the case of js/css/etc is bad
they probably set no-cache, which gives them the worst performance. and don't even use it for their benefit since they decide what to serve based on dns, which is always cached in the os and the browser.