Yes. It happens automatically if you let the Pogoplug go through the time consuming process of processing your media. Videos take a very very long time, btw. I am still scanning media after 20+ hours.

You can see the effect here: http://my.pogoplug.com/share/po4CKDEVRjwd_hA5kKZFVQ/

Note: Some of the files have been added or modified after I had started the video processing, that is why the thumbnails are not generated yet.