There is a small thread at WebmasterWorld with two advertisers complaining that their US based ads are not running as often as their UK based Microsoft adCenter campaigns. In short, the US campaigns they were running, in comparison to the UK campaigns, were getting a tiny fraction of impressions and clicks.
One advertiser emailed Microsoft and received this interesting response:
We see that your program was opened in 2006.
We see that you are receiving some impressions but not nearly as many as you could be. Sometimes when a campaign or ad group is not getting very much activity for a long period of time the ad will start showing less and less because it is not performing. That may be what has happened with your campaign.
My suggestion is to start two brand new campaigns and copy all of the data over from your existing campaigns.
We know adCenter has hit campaigns for low quality ranking factors in the past, but to have two campaigns, exactly the same, with the difference being UK versus US, that seems interesting. What I find even more interesting is that Microsoft here is suggesting the advertiser build a brand new campaign and just copy over the data.
Forum discussion at WebmasterWorld.