I'd like to track how much time I spend interacting with various applications and files on OS X. I found SLife in my search, but it is a web / subscription service. Is there any other OS X application that does something similar or better?
Time Sink by Many Tricks does this. It records running and frontmost application names, as well as the window titles of each application's frontmost window.
One downside of this approach I've found is that I often read a document in a background window because I can scroll through it anyway. I don't think there's a way around that issue, other than discipline.
It's generally not possible to record file interaction otherwise, since many applications close their file handles even though the user is editing or viewing the file in the application, only opening it again to save it, or load more data.