Oliver Steele, who is the Chief Software Architect at Laszlo Systems, wrote a short essay about the cost and time difference between “Explicity-Typed Languages” and “Implicitly-Typed Languages”.
A couple people pointed out in the comments that you gain back some of the time lost by developing types & tests in an Explicitly Typed Language when refactoring because your IDE can help you where it can’t in an Implicitly Typed Language. In my humble opinion, this (refactoring) is an example of one of the reasons why J2EE developers don’t look very long at ColdFusion. Moving to ColdFusion requires them to think procedurally rather than in objects (although CFC’s now provide pseudo OO behavior). Testing becomes stickier (although DRK 3 includes the CFunit component framework for testing ColdFusion components). Of course, Oliver’s article is also a great reason TO use a tool like ColdFusion. Instead of spending time writing recursively types,tests, & code, you can code/test/code/test.
Implicit typing makes initial development easier and faster.
On the other hand, it makes maintenance a bitch.
Thats one of the many reasons the LISP folks talk it up so much. You can develop prototypes untyped, and then type your interfaces once they are developed to enforce strong barriers ( which help maintenance ).