A Black Hat World thread has one webmaster noticing his rankings significantly shifted within the Bing search results over New Years.
Truth is, very few people would take notice of this being it is (a) Bing and (b) New Years day. But this one took notice, so much so that he emailed Bing to find out if there was a technical problem.
He said, Bing responded, which they are known for doing, saying nothing is wrong with the site - he has no penalties. Bing told him that it is standard for Bing to update their algorithm frequently.
I checked two rank checking tools that track Bing, both DigitalPoint and SERP Metrics and both show frequent fluctuations but nothing out of the norm over the past couple days when comparing it to the past 30-days:
Did you notice ranking changes over the past few days within Bing?
Forum discussion at Black Hat World.