Pinterest iOS engineers were asked to completely rethink and rebuild the iOS app - so they did not - no, of course, they did! That is what every engineer would want; an opportunity to be given some freedom to build.
They began to focus on performance, after all, the iPhone has the power with multiple processors. So their new app would rely heavily on the multithreaded code. Hmmm, what's multithreaded code you ask? I had no idea either. So I looked it up - in WIKIPEDIA, of course:
"In computer science, the term threaded code refers to a compiler implementation technique where the generated code has a form that mainly consists entirely of calls to subroutines. The code may be processed by an interpreter, or may simply be a sequence of machine code call instructions...", and so on.
I know, I know. It is got be correct/accurate if it is in WIKIPEDIA. It allows them to better maintain smoothness in scrolling and responsiveness when a user taps. Doesn't sound like much, but in testing, they got a 10X improvement in touch responsiveness (get your mind out of the gutter) and scrolled smoothness. Also, they've sped up scrolling by building the new framework on top of AsyncDisplayKit (ASDK). Which is an open-source IOS framework, authored by Scott Goodson.
Of course, what would the update be if it did not have some tweaking to the design? Never fear, according to Pinterest engineer, Garrett Moon, they took on the challenge, by building new animations and transitions.
The biggest notable change is apparent on the home screen. The new design will allow users to focus on their pins, (see below).
Download the app from iTunes.