The ability to collaborate with others is a key attraction for Google Drive and its associated office productivity apps, but tracking work across multiple files and projects can be difficult. A new Activity Stream shows you the most recent activity across all the files accessible on your drive.
The stream is accessed by clicking on the small 'i' icon in the top right corner (highlighted in the screen grab above). If you select a specific file or folder in the stream, you'll see a more detailed view of changes to that item.
As with most Google changes, this is being rolled out gradually so you might not see it immediately on your account. Google says it is going out to "everyone", so we assume Google Apps For Business users are covered too.
A new activity stream in Drive shows you what's changed [Google Drive Blog]