1. What are the current rules regarding transaction fees?
  2. What transactions are broadcasted by the QT-Client?
  3. How to the big pools act - what kind of transactions do say include in their blocks?

The background of the question: We are building a site where people can deposit bitcoins. Interact with the site to increase or decrease their balance and finally cash out to a Bitcoin address. (Like any Exchange, oder Just-Dice)

Obviously, we want to pay as little transaction fees as possible but still have reliable cash outs.

What is the best strategy to minimize fees?