As someone whose background is mostly in statically typed languages, who has been using Ruby and Rails for the past year, the biggest issue for me is when refac

As someone whose background is mostly in statically typed languages, who has been using Ruby and Rails for the past year, the biggest issue for me is when refactoring/making big changes to central parts of the app, the many repercussions of these changes often take a long time to track down, and subtle bugs are often introduced. By comparison, similar changes in a statically typed language are are usually much less scary, and less prone to having subtle breakage going unnoticed. A big test suite helps, but it's not a replacement for all the help a static type system will give you.