I found some interesting information while I was compiling this data. For instance, 5 of the 14 downward revisions came during a 2 month period from November 2009 to January 2010 and there hasn't been a downward revision since February 19, 2011. That means during Obama's time as President there has been an upward revision 88.2% of the time.
How does that compare to Bush? Well, in his last 55 weeks in office there were 8 downward revisions and 6 spot on estimates for an upward revision 74.5% of the time.
For a larger version click the images.