The Google Developers have released a chart outlining the current distribution of Android versions across all Android devices.
In the lead with a massive 55.5% is Android Gingerbread (2.3), which is the most recent version of Android (excluding Honeycomb and ICS) for phones (and some tablets). Second to this is Android FroYo (2.2) with a total of 30.4% of the version share.
What is good to see is that Android Honeycomb (3.0, 3.1 and 3.2) is now at a total of 3.3%, which shows that Android tablets are getting (gradually) more popular.
Android Ice Cream Sandwich has made a very small impact so far, with a total of 0.6%. This includes all of the 4.0.x devices.
All this data was collected within two weeks before the 3rd of January 2012. With CES hopefully bringing more ICS devices; and updates to existing phones and tablets, this will hopefully rise sharply.
I really feel sorry for the 1.6% who are stuck with Android 1.5 or 1.6.
Source: Android Developers