Over the next several weeks you'll see a new activity stream in Drive! The new Drive activity stream will show you not only which files have been most recently edited, but also gives you the option of seeing exactly what is being done. Once this change is implemented, the Details and activity button at the top right corner will open the activity stream. Select a specific file or folder and the stream updates to show information about that item. For more information on this change, see The Official update feed from the Google Apps team.
Update 3 Feb 2014: M+Google accounts will begin seeing this feature starting today. It may take a few days for all accounts to receive the update.