[STCrowley]

Hey, my advice is this: you can use the past simple almost always. At least, in American English. . . I teach a lot of Germans, and they want to use the present perfect way too often.

But, why do we use it? I tell my students that it has an extra 'feeling' of currentness (it is, after all, a present form) which means that it's the status SO FAR. For example, in the last ten years, I've lived in the U.S. and Germany. . . but the formulation means that I'm certainly not ruling out a move to Italy. (I hear they have better winters.) Or, if I say 'I've had a bad couple of days,' then I'm expressing that I'm still having problems but 'I had a bad couple of days' indicates that I think I've put it behind me and I'm moving on.

Does that make any sense?