The image on the left shows HadCRUT coverage in 1850. The image on the right shows HadCRUT coverage in March, 2011. In 1850, they covered less than 1/3 of the planet – yet report temperatures within 0.01 degrees.
Also interesting to note is that HadCRUT missed all the cold in Canada and Greenland last month, which explains their nonsensical uptick. At least they are honest enough not to make up data like GISS does.
The surface record is of very limited value, as the coverage is limited and erratic. Why did Dr. Muller not point any of these things out in his Congressional testimony?