Full site here: http://getmdl.io
Smooth scrolling seems to be broken on iOS. "-webkit-overflow-scroll: touch" seems to be missing on the main content if I had to guess.
It needs some extensive testing because there might be weird interactions with our layout component and all the different header modes it has (scrolling header, waterfall, etc). Working on it :)
edit: https://github.com/google/material-design-lite/pull/730