When I first began work in an office after Uni, I always said I would never do this, as its just recipe for trouble.
I've done it twice now, and its not been bad at all really. As long as you aren't a pleb about it, it can work out fine. The first one I saw for a good couple of months, and I decided she wasn't my sort so I put an end to it. We still speak and get on quite well. The second was more of a one night thing.
That said, I don't work on the same teams as either, so don't have to see them most days if I didn't want to.
Just go for it if you want to, my opinion has changed now. The office is a great environment for hooking up with people, you can slowly start to get to know people in a pressure free sort of environment.