Microsoft has reportedly sold 180 million Windows Vista licenses since its launch early last year. This translates into roughly 40 million copies since early May.

Microsoft said that 180 million Vista licenses have been sold since the operating system’s launch in late January 2007, which is a huge number by any measure. But given the criticism the software lately has received we were wondering whether demand for Vista in fact is increasing or whether it is stable or perhaps even decreasing.

Microsoft said that it sold 20 million copies of Vista in its first month, 40 million copies in its first 100 days and 60 million in six months. We have to be a bit careful with these numbers as they actually include Express Upgrade sales – a program that was available since October 26, 2006 and allowed Microsoft to take advantage of the Christmas season and sell Vista while it actually had no product available.

This current number of 180 million units is not directly comparable as it includes all Vista sales, including licenses via various volume-licensing deals.