It auto detects new movies when running, and if new movies are added while MediaPortal is not running, they will be added on launch. Same goes for removed files as well.
The only caveat is if a file's name is ambiguous and the importer can not find a match with a high probability of being correct, then you will have to go into the config screen to approve the match. In practice, this is a rare occurance though.
It did to a point, I noticed like quoted it adds them automatically on start, I transfered a file while it was running and it didnt add it, I let it wait for 20 mins both in and outside of moving pictures. It only appeared after restarting the application.
It would be good if it did what tv series did and prompted you to select one from within MP