Internet is a fast media. People would say a traditional web application is fast enough. But, once they experience some rich application, they’ll never think the same way again about traditional application. Using rich app in web design is so recommended.
Rich app allows netters to experience a more responsive internet activity. While traditional app load new page every time netters click on a link, rich app just send small piece of data to the already opened page. It leaves the page as it is, and update the relevant piece of the page This rich app greatly enhance web usability.
User will be able to enjoy a more interactive web experience. They can do more things more quickly. Some of the most popular rich app frameworks at the time are Flex, Ajax, Microsoft Silverlight, jquery, and many more. Each has its own strength and speciality. For example, Flex is flash based. It optimized the multimedia functionality, but not all browser starts with flash player plugin installed.
Anyway, if your mission is to build friendly user interface for your web design, call rich app for a help.