Like we wrote about this morning, one of the many advantages is that removing Flash as the video middleman can increase performance and reduce the hit to processing and download bandwidth as well as battery life. The player should load quickly, and you'll be able to jump the video playhead anywhere without having to wait for the content to buffer.
Although the feature rolled out today, it's still a beta test and might not show up to all viewers. To try it, load up the latest version of either Safari, Chrome or Internet Explorer with the Chrome Frame installed and look for a "Switch to HTML5 player" link below any video.
Vimeo says about 90% of videos uploaded within the past year should work with the new player, although 35% of the entire collection may still require Flash. The site will automatically switch for you and "always work" in either case.
Have you checked out the new HTML5 player? Let us know your impressions in the comments.