Normally when you receive a bluetooth in other devices the screen automatically bind up, but on N900 this not occur, so we can't see that someone is sending a file.

Not sure if there's meant to be a question in your topic or what, but on my device even if another bluetooth device is set as trusted, the N900 quite clearly asks for confirmation before receiving any file and gives you an "open file after saving" tickbox to choose, then asks you to give a filename to the incoming file and pick a location for it. AND then gives a "receiving complete" notification when the file has finished transferring.