I'd like to mention that I've been happy with the docs, once I learned to find them.

To take the given example, I would start at http://doc.rust-lang.org/std/ and hit `s` to start a search. Searching for `str::lines` gives http://doc.rust-lang.org/std/primitive.str.html#method.lines as the second result, which has the two methods conveniently next to each other, succinctly explains them, and shows an example of using each one.

I've had good luck with docs for the few third party libraries I've tried so far too. The recommended doc generation creates pages in the same format as the std docs, so as you get comfortable navigating them you get comfortable navigating many third party docs as well.