I create my user interface by creating a custom .Net application tailored to the customer.

Hey, just because I happen to still have it in my clipboard, I'll mention this book.

A simple report in a simple interface is a piece of cake.  Honest.  But, it can snowball into some really complex stuff, with what sound like simple user requirements.  So, don't be afraid to tell your users that you're branching into new territory here, and answer any new requests with "I'll see what I can do."