Google have denied the recent update in algorithm by making a sweeping statement that they make over 500 changes a year.
As a company who are monitoring 24/7 we can safely say that there was a pretty major update which came affected rankings on 17th January 2013.
If your SERPS have disappeared for your keywords this is why. Of course as always there will be winners and losers.
When the dust has settled our SEO team have had chance to gather data and analyse it we will be able to shed more light on it.