How to deal with files
 

A main purpose of GTD is to get everything out of your head into a trusted system.
For most who use a software based implementation of GTD, that involves one single file to hold everything to avoid misplacement of "stuff."
If OmniFocus is to be a Productivity App it is interesting to think of an app whose focus (no pun intended) is to really only handle one file. As a result of this the typical concept of an app doing "one" thing on multiple files is turned on its head, and instead multiple tasks and events need to be done on one file.
Just a thought.