iAd slowdown?

Since I started developing for iOS I used iAd and I was always satisfied. Ads were graphically clean, fill rate (i.e. requests accepted by the network on the total number of those generated by the app) was always above 75% and there were relatively high revenue for impressions and/or clicks. In the last few weeks, however, something is changed...

At the end of the holiday season, specifically from January 6, there has been a dramatic decline in served ads. My experience is based on a particular audience: 76% of the requests from my apps comes from Italy, 9% from U.S.A. and the rest is divided around the world. To better understand this fill rate decline look at this chart:

iAd fill rate - January 2013

As you can see it had a good value (over 70%) in the last days of December and then went down to a scanty 15%. Unfortunately I have no way to know if it is just a temporary problem maybe related to a rotation into the ad inventory or if it is a real unbalance between publishers and investors...

For now I'll just wait. We'll see next month if something will change, otherwise I will decide whether to batten down the hatches. Is there anyone else who is experiencing the same thing? Do you recommend me other ad networks as primary choice (AdMob, MobFox, LeadBolt, etc.)?