Twitter's redesign is one of the most performant SPA's I've seen in a while. It's really smooth and nicely designed too. A lot better than their previous webapp.
For their infinite scrolling, they clean the DOM above and below the viewport and only keep a certain amount of tweets rendered. So once you start scrolling a little faster, the JavaScript can't keep pace and starts sputtering.
Do you know any others? Every time I’m redirected to twitter on mobile I’m in awe, it’s genuinely the only SPA I’ve ever experienced work “properly” on my phone comparable to a native app without any polish.