It seems strange to still be discussing Y2K Bugs in 2007. But as this is historical data so it’s no big surprise.
It seems that US Climate Data from NASA had a Y2K discontinuity that caused some recent years to be recorded as hotter (in the US) than they should have been. NASA has apparently now fixed the discrepency. The new data now ranks the top ten hotest years in the US as (in order from hotest) as 1934, 1998, 1921, 2006, 1931, 1999, 1953, 1990, 1938, 1939.
What’s the significant’s of this? Scientifically, nothing. Politically however it presents a public relations problem to people supporting anthropogenic global warming.