I made Guinness ice cream this weekend. It's amazingly good. It's made with Guinness, of course, molasses, and the regular ice cream ingredients. Highly recommended. I was telling a guy here at work about it, and he said the best ice creams are made with molasses, and I believe it.
I got the recipe from this site. She used the ice cream in a float with Harp - aka a black and tan, only with Guinness ice cream as opposed to Guinness itself. I haven't tried this, but it also sounds delicious.
So we're up to two things I make with Guinness - beef roast and ice cream. Both are very good. Can cooking with Guinness be wrong, I wonder? I think not.