I've been looking at historic GDP data as posted here:
http://www.eh.net/hmit/gdp/

I found that Real GDP has risen about 3.6 percent (on average)
annually throughout the history of the United States.  I also found
that real GDP rose only 3.2 percent (on average, annually) between
1990 and 2003.
http://www.csua.berkeley.edu/~darin/images/lnGdp.png

What has caused the relatively sluggish growth in the US economy over
the past 13 or so years?  Should I expect the growth rate in future
decades to be 3.2 or 3.6 percent, and why?