>For example I am putting in 900 hours of development time creating forms and screens. What percentage of the 900 hours should I build in to allow for user feedback on how this forms and reports should be changed?

well this is sort of a blind question Evan. But if it was me...

If the users were intimately involved when developing requirements, functional specifications, and use cases I would be comfortable formally estimating somewhere between 10 to 20%. If the users weren't heavily involved upfront, I would estimate it at 75% just to cover my butt.