Vimeo is playing around with thumbnails on the site and experimenting with a new animated feature for some of them. With just a few live at the moment, it's hardly a site-wide roll-out but they are testing out animated thumbnails on some of its "Staff Picks" until they decide how to proceed. Those staff-picked creators will be asked whether they want an animated thumbnail, so can refuse, and not every video featured in that section will get one - yet.
Vimeo is asking for feedback in the comments of this blog post. Have a look, see what you think, and let them know. We like them, it would be great to see a wider roll-out.
Here's one of them in action below, for an animated short titled Transmission.