Mobile web applications will be easier to develop and deploy. Developers will not need to learn new technologies or create different applications depending whether the target platform is a mobile device or a desktop computer. They will have a full control whether the mobile device is on-line or off-line and with the increasing popularity of iPhone / iPod Touch touch and Android, they will be sure that their applications can reach a big slice of the mobile market.
If you browse the web searching for explanations and samples about the new features of HTML you will find a lot of articles with detailed information about it. I will only comment the most interesting features that in my opinion are focused for rich featured web applications. I recommend browse the samples published in HTML 5 Demos and Examples by Remy Sharp.
- Local Storage. With this feature web applications will be able to store locally in the client side data as application data or session data. This local storage can be very useful to let users work off-line and submit all the work done when the device is on-line again without losing any piece of data.
- Input element improvements. For data centric web applications, data type input, and validation will be easier and integrated with the web browser without external libraries. Unfortunately, the support of this feature in current web browsers versions is very poor.
- Geo-localization. Very interesting for mobile applications. With this feature, web applications will be able to offer data to the user contextualized in the place he or she is.
- Webworkers. Using this new feature developers will be able to implement background processes in the client side leaving the application responsive to user actions and without blocking him.