Just for the novelty factor, I've used the top surface of my Roto-Broil for heating up whatever contents in a saucepan, but that's about it. You have to raise the top cover when roasting anyway, so the hot surface is there for the using.
Also, that surface temperature varies with the roaster's temp setting, which means you get what you get. Even on High setting you couldn't seriously boil water for pasta up there, but for things that only need to be heated through, it's fine.
I would not attempt the level of cooking pictured in the product literature, that's for sure.