Not all economists and economic experts believe the U.S. economy is improving.  For example Comstock Partners has this to say:

Although the market celebrated today’s releases on weekly unemployment claims and the ISM Manufacturing Index, the trajectory of this weak economic recovery has probably not changed.  Both of these indicators are affected by the difficulty the government has in gauging the seasonal adjustment factors in this part of the year as a result of the timing of the annual auto industry shutdowns for re-tooling.  In our view, the 1st and 2nd quarter GDP results offer a much more representative outlook for an economy that seems to be losing steam rather than picking up as most observers believe.

The GDP results for the first half are a more accurate indicator of how weak the economic recovery has become.  An unexpectedly large rise in inventories accounted for 24% of 2nd quarter growth, while consumption was up only 1.2%, compared to a still anemic 1.5% in the prior quarter.  Final demand was up only 1.3% in the 2nd quarter and 0.3% in the 1st.  The need to work off the excess inventories will tend to impede second half growth.  In addition government spending was down less than expected, indicating that further layoffs related to the sequester are still ahead. 

My observation is that I am not sure whether Comstock is correct or not.  But, it does seem our economy is growing but growing at a slower pace than during economic rebounds in the past.