Why Static Typing Matters

A powerful argument in favour of static over dynamic typing is that the former can allow you to catch a whole class of thread safety errors at compile time.  From a post by Trevion at Nonlinear:

Recently, I've had some fun discovering which parts of the .Net libraries are threadsafe.  While reading the documentation would have helped my quest, and testing did discover the non-threadsafe functions I'd missed (granted, four hours into batch runs), in Haskell I'd have been able to tell from the types whether or not the operations were threadsafe.  That's a stronger assertion than I've seen any testing library be able to make.