[mikekchar]

I think the key is that showing progress early and often lets the customer start to get a feel for how long the entire process is going to take. This is one of the reasons for XP's idea of trying to do "vertical" but narrow slices of the application. Each story you work on should work through as many layers of the application as you can manage.

It's easy to write stories that are "do the UI for X", and then "do the back end for X". But often the UI (at least the first cut) is easy to code and comes out quickly, giving the customer the impression that everything will be quick. Then you work on the back end and it goes a lot more slowly, leading to mistrust. Alternatively, working on really complicated things up front (while generally a good idea) can give the customer the impression that the project is stalled and that it's never going to finish.

When you are doing iterative development, I think the real art is in choosing your stories. It's difficult, but when done well it removes most of the political friction in development.