AdMob, the company which places ads on websites targeted at mobile users and which has just been acquired by Google, has published the results of a survey into app downloading, buying and usage habits. While the survey was quite small – under 1,000 people who opted-in to the survey – the findings were interesting. iPhone and Android users both downloaded just under 9 apps per month on average, but both were outdone by iPod Touch users, who averaged 12 apps per month.  And those iPod apps also get more use; an average of 100 minutes per user per day, compared to 80 minutes for iPhone and Android.

When it comes to actually paying for apps, Android users average just over one app per month, with only 21% of users buying anything; iPod Touch users average 1.6 apps per month, while the iPhone leads the way with 1.8 – and with 50% of users buying at least one app per month.

The number of ads served by AdMob continues to grow at an astonishing rate; in January, over 7.3 billion ads were served in North America, a jump of a third over December 2009. That rate of growth may slow in the coming months – all those Christmas presents are sure to have caused a spike in January demand and usage, which will likely drop off a little in February. The iPhone and iPod Touch accounted for a whopping 40% of those ads.

What does all this mean? It’s a good indication that the apparently insatiable appetite for apps shows no sign of slowing, and that the rise of the smartphone has yet to get anywhere near a peak. The marketing opportunities presented by providing branded apps, or by using mobile advertising, are ones that companies ignore at their peril. You can find the AdMob reports here.