I used to have an Australian girkfriend who would ask "did you eat yet?" which really threw me (as a Brit) while it makes perfect sense logically, i needed the use of prsent perfect to make the link between past action (at an unspecific time) and present situation clear. i.e. have you eaten at some point oday and are you hungry now?

So although both simple past and PP are fine in the inital sample sentence, I would always lean towards "have you sent the files?", however whe teaching my english classes, I would also teach both as acceptable uses.

Joe
www.lse.uk.net