The Americans and the darned present perfect .....

 I think the mistake many English learners make is that they draw a line of separation between British English and American English, believing it best to focus on learning one or the other. In reality native speakers do not differentiate between different types of English, yes we are aware of the different English accent from around the world, but to us, it's all just 'English'.
I get asked many times about the difference between AE and BE, so I thought I would take five minutes to talk about the 'infamous present perfect'. It's untrue when people say Americans don't use the present perfect (I have lost my keys ...), however they do have a different idea of time; we teach that if the event still has an effect on or is connected to 'now' (eg "I've eaten too much for breakfast" - with the effect being that now you have stomach ache) then we tend to use the present perfect (British English), however Americans have a different or narrower idea of 'connection', so they think 'this morning' (even if it's still part of 'today') is finished and so they tend to say "I ate too much for breakfast, and now I have stomach ache". But it is still widely used in American English, just in slightly different circumstances, so yes you still have to study it