I'm very bad at faces. After I've been introduced to someone new, I'll have to meet them another half a dozen times before I recognise them by sight. And even after that, I can be thrown by seeing them with a different hairstyle, or wildly different clothes, or somewhere where I didn't expect to see them - ie, I might have reached the point where I'll recognise a colleague within my place of work, but if I then saw them in a store, I wouldn't recognise them.
Like krex said, though, I'm usually quite good at recognising actors on TV, maybe because you spend so much time looking directly at them. I can visualise my favorite actors in my head, whereas I have difficulty bringing up a picture of someone I know in real life.