Emily Kirk, a Rimm-Kaufman Group analyst spotted a feature Microsoft is testing with Bing: paid results in the middle of organic results. Yep.
Ordinarily on Bing, paid ads appear above and below organic results, and they're easily identifiable in a blue box:
The test feature eliminates the blue box and sticks them in the middle of the results, making them far less distinguishable as ads, though there is still a an "ads" label off to the right.
Image credit: RKGz
Barry Schwartz at Search Engine Land obtained the following statement from Microsoft, "We’re constantly testing and experimenting on Bing, and with that, we carefully measure user engagement and reaction to these changes. We have nothing further to share at this time."
I'd be very surprised if this moved from testing to become an actual feature, because there would be a fair amount of negative publicity I think. It's become pretty well established throughout the industry that paid search results should be very clear to the user. That said, perhaps Microsoft considers the small "ad" label to be sufficient.