How does Google determine Android version percentages? Why, by monitoring what phones accessed Market in the fortnight leading up to yesterday, November 1st.
The figures aren't going to be completely accurate (not everyone will have looked at the app store in those two weeks, for example), but when carriers take their sweet time releasing OTA updates and users can easily root their phones, it's going to be the closest we get to true numbers.
Interestingly, 77 per cent of devices are now running Android 2.1 or 2.2 (Eclair or Froyo), with Eclair being the most-used Android version with 40.8 per cent of users running it. Android 1.6 (which a lot of phones are still running, distressingly), has 15 per cent of the pie.