I noticed several websites using a fullscreen background videos on their home pages. A good example is Paypal.com. The videos are typically short, between 10-15 seconds, with the sound turned off. The video falls back to a still background image for visitors whose browsers do not support HTML5 videos.
In addition, Paypal is using what looks like a playlist of several short videos that are displayed in a loop. If you’re interested in how you can implement background videos on your web pages, demothenes.info has a tutorial on how to add video background videos on your website.