Google just released the latest figures on the number of Android variants in the wild. For the two weeks ending Feb. 2, 89.8 percent of devices are on Android 2.1 and up. Realistically, that means Android 2.1 and 2.2 -- Froyo leads the way at 57.6 percent -- as only 0.8 percent are running Gingerbead. That gives you a feel for how few Nexus S's have sold.
Android 1.5 and 1.6 are down to 3.9 and 6.3 percent, respectively. [Android Developers Blog]