AdMob has been using its in-app advertising services to analyse the adoption of the new 3.1 OS in the weeks since its 9th September release.

Adoption has been speedy with 23 percent of ad requests coming from OS 3.1 devices, although as the update was free for everyone with OS 3.0, perhaps that's no surprise.

The bulk of devices - 51 percent - are on OS 3.0, giving a total of 74 percent on OS 3.x, which is good to know for developers planning on using micro-transactions.

As for the laggards, 19 percent are on 2.2.1 and 7 percent still on 2.2.

As for the split between iPhone and iPod touches, AdMob says 91 percent of ad requests from iPhones are from OS 3.x devices, compared to only 35 percent of iPod touch requests.

Lets hope Apple sorts out the legal issues that have forced it to charge for updates; OS 3.x is currently costs $5/£3.

[source: AdMob]