In my experience I lose less time specifying that an argument is a string in Go than I do adding a test to handle the possibility that nil gets passed in Ruby.
i appreciate type checking so much more now than i used to, and i find that i disliked it most when i needed it most (i.e., i blanched at it more when i was a worse programmer, even more likely to make type errors than i am now).
there are categories of checks in application code (as well as whole categories of simple unit tests) that i just wouldn't have to write with a static type checker. additionally, as other comments have pointed out, it'd make it easier to automatically refactor things.
i started coming around on it with groovy a number of years ago (after sorta hating the type checker in java/c/c++ for years before that). i'd find myself writing a bunch of untyped code, but then i'd also find myself going back and specifying types as i wrote tests, because it was often easier to just specify the type than to write a test for the possibility of the wrong type coming in.
as someone who mostly writes ruby code these days, i'd love to see an optional type checker get added.