37signals recently posted about using PJAX and server-side templating to rebuild Basecamp.

Theres a counterpoint of linkedin moving towards client side with dust.js: http://engineering.linkedin.com/frontend/leaving-jsps-dust-m...

But I'm also interested in hearing about twitter/githubs change of heart.

No, they didn't. Pop the inspector's network panel open and watch what happens on Twitter. All the content comes down as JSON.

The claim is that they in the process of switching back, not that it's already rolled out.

They were switching from hashbang routing to pushstate, not from client to serverside rendering. Although they might to pre-rendering for IE, which will get support of pushstate only in version 10.

http://storify.com/timhaines/hashbang-conversation

Hopefully they are going with pushState with a fall-back to server rendering for all user agents that don't support pushState.

That's a compromise I can get behind. And it's pretty much progressive enhancement...

I thought they were simply changing over to compiling their mustache templates on the server to speed up the process.