After introducing the Maps Plus Box and testing the Finance Plus Box, Google experiments with a Video Plus Box that shows a preview of a video inside the search results. Razvan Antonescu, who spotted this experiment, saw it only for a Google Video page, so it's likely that - at least for the moment - Google will add it only for Google Video and YouTube.
Of course, Google should continue to be objective and include it for all the online video sites, but there are some questions:
* What are the videos sites? How to detect all of them and find the embeddable code?
* Will those sites want the Plus Box? Maybe they'll say Google steals traffic from them, because they want to show ads and to have big page views.
* Who will click on the search result to see the video (and maybe some comments and context), like they used to do?
* It will be the first time when content outside of Google control will be included in the search results (for example, the thumbnails from image search results are hosted by Google). Will there be performance issues?
Google also promised to add more video sites to Google Video and to transform it into a real video search engine. They'll have to answer to the same questions for Google Video, so they should connect these two efforts to make videos more accessible.