The query Amir Blumenfeld shows thumbnails next to a blog that occasionally posts videos and next to a "tumbleblog" that mostly consists of videos (the first and the seventh result from the screenshot below). The videos are hosted by other web sites (in this case, Vimeo) and the thumbnails are only included for homepages.
Google added thumbnails next to video search results as part of the Universal Search program that blends heterogeneous results from different specialized search engines. While the thumbnails sometimes help to describe a video, they also attract your attention as they're one of the few non-textual parts of the page.
It will be interesting to see if Google will eventually show different snippet formats depending on the type of a site (for example, Google could show the author of a blog, the date of a research paper, thumbnails from a photo album or the price and other information about a product).
{ via Googlified }