Wow, this is fast. About 70% of all active Android phone users are using Android 2.0 or higher OS, based on Android Developers’ report.
So, if you are still using Donut (Android 1.5) or Cupcake (Android 1.6), I think you are way behind. BTW, if I remembered correctly, Sony Ericsson Android phones are still using Android 1.6. Hopefully, they can skip OS 2.1 (Elcair) and go direct to OS 2.2 (Froyo).
Here is another graph to show the distribution against the year.