We covered this before but it probably should be pulled out as its own post here, the popular products carousel snippet for web sites that have products that they deem popular on their web sites. We covered it last week, here is the screen shot from Valentin Pletzer on Twitter:

Here is another one from Cindy Krum on Twitter:

I suspect it has to do with the Google product markup changes from a week or so ago.

Forum discussion at Twitter.