Tests and rails
I discovered that in the presence of SelfTestingCode, most bugs that static types would have were found just as easily by the tests.
Last night I was playing with rails trying to understand some of the features. Old habits kicked in. I did not write some tests and got bitten once again. Lost almost an hour on a few stupid typos. As Martin Fowler explains, tests are more important in a dynamic typed language as the compiler won’t catch some errors for you. Fortunately, rails supports testing right out of the box.