Read here and here. With Climategate exposing fraud and the leftist-liberal, anti-science agenda leading up to Copenhagen (COP15), attention is starting to focus on NASA. The climate researchers at NASA's GISS have funding incentives that promote a global warming agenda, which does not make for good science. Certainly GISS has had its share of temperature data presentation problems/issues and very questionable science techniques.
Here's an example of GISS using selective data in the chart starting at 1900 to promote the warming agenda. But if the entire temperature data record is shown from the year 1820, warming actually becomes cooling. (click image to enlarge)
And, here's an example of GISS 'cooking the temperature data books' to manufacture non-existent global warming. They "adjust" earlier temperatures down and "adjust" later temperatures up to produce a warming trend that is more dramatic. (click image to enlarge)