Before I switched over to full time software development,  I used to write functional specs for some of the applications at ATG. The most frustrating aspect of this wasn’t the text itself, since describing what happens when you click a button is pretty sweet, but being blocked waiting for the UI designer to update the wireframe models. He and I used Microsoft Visio, a bulky, awkward product on a good day, and we lost quite a few days to his creating prototypes. (It didn’t help that he was three time zones away.)