http://stackoverflow.com/questions/3649969/what-do-you-think...
No source for bits of it which makes it risky since it seems there's only one guy developing it.
Looking at it's comms it seems pretty lightweight, though it does generate a lot of messages.
Last time I looked the Sencha library it used was fairly old
That said if you've got a low-medium weight web app you want to build and don't care if it looks like windows, then it's dead easy (really 1 day or so, it's that easy).
Edit: maybe it was per seat licensing? - client didn't want that
we need sometime like, for polymer one day?
At every Google IO they presented it, and yet the overall native support of all required features without any kind of polyfills is still missing across all browsers.