Adobe just announced at the Google IO 2010 event at Moscone Center in San Francisco that Dreamweaver CS5 will support HTML5 by use of download of a new extension that just became available at Adobe Labs. The new extension will provide features to help users generate HTML5 and CSS3 code. Features include Multiscreen Preview, Media Query support, code hinting, starter layouts, and WebKit updates for rendering enhancements. You can learn more about these new features here and download the extension here.