It seems that NBA 2K11 has now shipped 5 million copies.
Source: http://www.vg247.com/2011/05/23/2k-signs-multi-year-extension-with-nba/VG247 said:2K signs multi-year extension deal with NBA
Take Twos announced an extension of its NBA deal, which has seen NBA 2K11 sell 5 million units worldwide.
The new deal is a multi-year offering, and follows the success of 2K11, which is the most popular NBA 2K title in the series 13 year history as well as the best-selling title in 2K Sports history.
Take Two says 2K Sports will explore new NBA licensed gaming opportunities, including online and social media platforms.