Did you know that Revit has a lot in common with the NSA?
Revit tracks a lot of the moves that you make within the software. One of the reasons Revit does this is to track down issues when a model crashes. This information is stored in the Journal file.
One other thing you can try to do with Journal files is re-trace your actions. Say you are working in Revit and 20 minutes after your last sync to central, Revit crashes, in therory you could grab the journal file and \ drag the journal file onto the Revit shortcut on your desktop. Revit will open and run the journal file opening the file you were working on and running repeating your previous actions like a macro of script.
In theory this works, in practice its not that simple. But it is possible. Many of the Revit benchmark tools that are available use a journal file to time and record a series of tasks. Using a Journal file to restore lost work is more luck than anything else.
You can also use the Journal file to see what work has been done and it is something that is done to diagnose why Revit might be crashing.
In Winows 7, the Journal file can be found at: %LOCALAPPDATA%\Autodesk\Revit\