HTML 5 features which are useful right now include:
1) Web Workers: Certain web applications use heavy scripts to perform functions. Web Workers use separate background threads for processing and it does not effect the performance of a web page.
2) Video: You can embed video without third-party proprietary plug-ins or codec. Video becomes as easy as embedding an image.
3) Canvas: This feature allows a web developer to render graphics on the fly. As with video, there is no need for a plug in.
4) Application caches: Web pages will start storing more and more information locally on the visitor’s computer. It works like cookies, but where cookies are small, the new feature allows for much larger files. Google Gears is an excellent example of this in action.
5) Geolocation: Best known for use on mobile devices, geolocation is coming with HTML5.