It's always valuable to learn a new programming language. And both Python and Ruby are good ones to know. It's important to note that while Python is a language, Ruby on Rails is a framework. IMHO, you should learn Ruby before you learn Rails.
Go try ruby! to see if you like it. If you do, then try Rails. Otherwise, try Python. Both are similarly useful. To me, Ruby is more "fun". If you like Lisp, you'll probably like Ruby. If you like C, you might prefer Python. Try them both!
