After leaving Ruby (non-Rails) for Python this year, I've mostly noticed the difference in the obsession about testing. The Ruby crew is very into TDD (and now BDD)–that isn't to say that Python folks don't test (or do TDD/BDD), but simply that the tools available in Python aren't quite as polished. Ruby's RSpec, RCov, Flog, Autotest, & Heckle are all quite wonderful. I do like Nose, but get annoyed by lack of friendly code coverage tools in Python.