Concerning the Input Assistant, Ctrl+K now invokes the completion menu.
But the completion menu comes up automatically when you need it, and
invoking a completion is as simple as pressing Enter or Tab. I, for
one, didn't really use Ctrl+K all that much before, but I am using this
all the time, now. In observing other people use Mathematica, I see
people getting used to using this very quickly, and it being very easy
to adopt. There are a few tweaks we could stand to make, yet, but it
seems to be a big win for everyone I've seen.