If a user saves an ai file as pdf (for example) and a "view pdf after saving" is selected, the pdf opens in Acrobat - but, the file DOES NOT update if the pdf is left open and the file is saved over. I personally do this probably 20+ times a day as a I tweak a file.

Acrobat could have a setting "update open files." Many of us use acrobat as a final visual proof before sending to clients, currently we have to close, open/find to view files after save-overs.