A fairly hot topic at the moment is with drawing revisions, specifically how to track revised changes within Revit. Currently there are no features within the Revit software to compare changes to drawings from one revision to the next; however, Autodesk Design Review 2012 does have some of the answers!
Autodesk Design Review can see the differences between 2D drawing views and uses a very simple ‘traffic light’ system to track the differences between two drawings.

There are a few exceptions to what Design review can check and I have included these in the table below.
To start checking for changes you will need to have DWF versions of the sheets before and after the changes have occurred. You can then open the original DWF version and then use the following ribbon to compare sheets.

In the image below I have made a change to the section size of a rafter and changed Level 2. Both of these have been identified within the DWF file shown below.

You could of course use this to check the differences from any 2D drawings.
Hope this helps,
LawrenceH