@ottovirta
Head of web experiences
Foodie.fm
HTML5 is widely supported in desktop browsers and modern smart phones like Android and iOS-devices. There are also a lot of polyfills that can be used to add missing features. However if you need to target any of the older phones you won't be able to take full advantage of the new and shiny features of HTML5...yet.
More than 2.1 billion mobile devices will have HTML5 browsers by 2016, up from just 109 million in 2010, according to a report by ABI Research. (http://gigaom.com/2011/07/22/the-html5-boom-is-coming-fast/)