One other tip that the KC Hyatt taught me the last two stays:

Do NOT surrender the certificates in advance. The same completely clueless front desk clerk two stays in a row in a period of 3 days gave me grief for not surrendering them up front when I checked in. (She also didn't know how to process them, and had to get a manager both times)

She insisted over and over that I needed to hand them over up front when I checked in. I responded back that
1. Hyatt is -not- a gas station in a bad neighborhood. One shouldn't be forced to pay cash up front at a decent hotel.
2. I've used them at about 10 properties, and have never been asked to do that before. What makes the KC property different?
3. How am I going to guess what my exact total is, with room service and other charges? Is it like the gas station in #1?
4. What if I check out early and you've already endorsed/lost/filed them? I'm not that stupid to leave a couple grand in cash for them to "hold", either.