Learn at least one new language every year. Different languages solve the same problems in different ways. By learning several different approaches, you can help broaden your thinking and avoid getting stuck in a rut.
So true. It does change the way we think and code. But learning a new programming language is not just reading manuals, books, tutorials. That is not going to help. Executing the sample code is not going to help either. ( it did not at least for me)
Unless solving a real problem or working on a real project its not going to help learn the language.
IMHO solving problems listed in projecteuler.net helps a lot in learning a new language.
I have just started writing solutions in Scala and Ruby and IT IS helping me a lot to learn these two languages.
I am also learning Python, and Clojure is next in the to-learn list with Haskell and Erlang.