I wrote a long detailed post about the effectiveness of buying my AdMob ads. I had contacted admob about it. Well it seems they wrote their own blog post about the average conversion rates they see for admob ads. I don’t feel the need to post mine anymore as long as this post is available.
All developers thinking of buying traffic from AdMob, take a good look at the 1% conversion rate for clickthroughs they have posted for paid apps. Then decide for yourself whether this is effective for your own app in any ad buys you make.