Joshua Ledwell has it right with his short post on iterative user interface design. 

In my words:

Someone once said Fail early, fail often… Early means UX people should iterate wireframes over and over again!

It is very important to communicate this to partners and clients clearly at the start of a project. It can take a while for them to understand that your wireframes are not going to be perfect straight up! This is particularly true of rich applications - the possibilities of interface design are infinite!

At the early stages of the project the wireframes lead to innovation, they trigger ideas and requirements that were not previously considered. This is particularly for new products.

Iterated wireframes also allow each member of the project team to ’show’ us their perspective. You know, many minds are better than one (UX) person!