Occasionally Google produces charts showing "the relative number of active devices running a given version of the Android platform." The latest of these charts is special though: It apparently marks the first time Android 2.1 was the most used version.
Click on the image for a closer look.
It's worth noting that this data was compiled "based on the number of Android devices that have accessed Android Market within a 14-day period." So don't run off shouting about the death of any Android versions older than 2.1 just yet. [Android Developers via Android Police]