also has clear benefits for your users. They get a browser-native video player, which can potentially be very efficient. They get a consistent UI that won't change from site to site. Mobile browsers that may not implement flash can still implement .
The only con is a temporary one, and that is compatibility. IE8 doesn't support , and it will be some time before IE9 is widely installed. As well, there's some fight over which codecs to support for the videos - Firefox, Chrome, and Opera all support both Ogg Theora and WebM, while Safari and IE are shipping H.264 (though either can support Theora/WebM with proper codecs). For now, this just means that you have to post your video in two formats and provide them both with the source element, i.e.:
To add support for IE 8 and earlier, and other downlevel clients (like older versions of FF/Safari/Opera/etc), just put your standard video embed code inside the tag, below the elements. If the browser supports , it'll ignore the embed. If it doesn't, it'll ignore the and run the embed instead.