Do you remember a Google Blog post from mid-July where Google Video's, Matthew Vosburgh, announced that two "radio buttons" were available allowing a searcher to limit their Google Video search to only playable video or both playable video and video clips where thumbmnail images were only available? Well, it appears that this useful search option is no longer available Why? What happened? Will Google bring it back? How about letting us know with an explanation on the Google Blog? Here's a cached copy of what the Google Video interface used to look like with the search options (via Gigablast cache).
However, it is still possible to limit your search to only "playable video" using this "hacked" interface or the syntax source:upload or playable:true in your query. More about both tools in this post.
Postscript: A reader correctly points out that in many but not all cases Google Video results now show playable video before non-playable video. Still, having an option without having to limit to a certain type of material without needing to use the syntax would be useful.