Froyo is installed in more devices than any other Android build
Surprisingly, 3.5% of phones running Google's open source OS are still powered by Android 1.6 while 2.7% have Android 1.5 under the hood. But what about the newer Gingerbread versions? Android 2.3 can be found on .8% of Android phones while Android 2.3.3 represents 1.7% of the outstanding handsets. The Honeycomb build, optimized for tablets, is on .2% of Android devices.
As time passes, you can expect the older builds to start dropping off in numbers and as Android users start to replace their older models with newer dual-core, 4G enabled phones, we should see the majority of Android phones running Froyo and higher. Considering the features that Android 2.2 brings to the table, it will be some time before that build starts to drop off significantly, but the percentage of devices running Eclair should drop sharply as 2011 comes to a close.