HTML5 is here, merely supported by all popular browsers, including mobile ones like the Safari on iPhone. This new standard is a huge step toward turning the web into the ultimate platform. Complex applications that needed native code for each operating system can now be replaced with platform-independent web applications. Just think of Google Earth - you can really have it in your browser.
Considering my favorit area of web development, the GeoWeb (meaning social web apps with geospatial contents), what are the benefits of HTML5? Let me mention only two of them
1 - The "canvas" tag lets you manipulate vector images from scripts. Have a look at this example
2 - The geolocation API lets you reach GPS data right from the browser. My favorite web application of this kind is the Latitude from Google. The image in the top left shows a screenshot of Latitude running in the browser of an iPhone
So, now we can create even vector-map applications with GPS support simply in HTML!