According to the latest data Google have taken during a 14-day period ending on September 4, Android 2.3 Gingerbread still rules the roost with 57% of devices running the ageing mobile OS. Android 4.0 Ice Cream Sandwich sits in second place with a little under 21% of Android devices.
Google's latest Android 4.1 Jelly Bean OS isn't doing too badly, with 1.2%, but this should grow quite rapidly with more and more new devices being announced with the OS on-board. Android 3.1 Honeycomb is sitting with just over 2%, and was a release-and-forget-it OS from Google, as it was only on tablets, and was definitely not popular at all.
Ice Cream Sandwich adoption has been growing rapidly in the last six months, from 1% or so to its current 21%. The last three months in particular have been great for Android 4.0 ICS. I'm expecting Jelly Bean distribution to go from 1.2% to around 4-5% by the end of the year, and ICS to jump to around 30-40% in this time. Gingerbread will probably drop from 57% to less than 50% in this time.