Note: this is mouser's idea - i just thought it might be worth trying to get the ball rolling on it.
i wonder if maybe it would be interesting to have an app like "Recent Document Timeline" which showed like a timeline of usage of documents so you could see when you used each document and which would help you locate documents based on how long ago it was that you last opened them.
i'm not sure about other programs but 'Adobe Album' has a timeline feature for displaying images which seems a bit strange when you first encounter it but can be quite useful when you get the hang of it.
'ACDSee' has a similar function but works in more of a calendar type of way, so it's probably a common feature of image manager programs.
expanding on mouser's original idea i think something along the 'Adobe Album' timeline approach could work well. as it works in quite a visual way it's very quick to use. i'm sure there are many enhancements that could be incorporated into such a util.
the slider bar mechanism works well in 'Adobe Album' allowing you to easily select start and end dates to constrain which files are displayed. this obviously needs improving a little to include start and end times but i think it would be a good feature to build upon.
i think mouser must have a time machine because i think it's easy to foresee that this type of feature is going to be common place in all kinds of apps in the not too distant future.