The Internet has had a profound impact on user expectations. Not too long ago, a computer user was a highly trained individual. Businesses trained their users to be experts in one or two specific applications. A Web user, though, is an entirely different breed. A business doesn't have the luxury of training its Web users.
Web applications have to be intuitive.
Or perhaps it's more appropriate to say that Web applications have to be invisible. The user doesn't view these activities as executing applications. The user is simply using services that are available on the Web. The user wants to be able to access these services from a wide variety of client devices, such as desktop systems, PDAs, mobile phones, and in-car computers. Furthermore, the user wants these services to understand and act differently according to the context of the situation.