Diamond upgrade cert question
 

Can I use this for more than one room at the same time. I.e if I book both rooms and then use 2 certs to upgrade both (obviously I'd only be using one myself).

Nope - I think you can only use one per reservation. I'd call to inquire w/ the Diamond line, but I'd bet they shoot it down.

I've heard of some Hyatts giving both rooms the Diamond benefits (free breakfast, internet, etc.). Very much a case of YMMV from what I understand.

I've had it allowed for me before. It may not be required, but hotels may do it.