Evolving the UI

"When using agile methods, it is not uncommon for the contents of a release to change dramatically. This can create problems for up-front user interface design as it is created with the expectation that certain functionality will be present in the released system. As UI design is created across features using techniques such as scenarios, it is especially vulnerable to changes. A user interface design also assumes that functionality will be implemented in an order that makes navigating from one feature to another possible. However, if the customer's priorities do not match the flow created by the UI designer then the design may have to change substantially.

Fat client UI frameworks still need a lot of work to get to the point where they are as adaptable as web applications. The main argument in favour of fat clients is the richness of interaction that you get from native client controls. However, with the rise of GMail style applications and the rebirth of Javascript, this may no longer be the case." (Via Lost on the Subcontenent)