I'm mildly face blind. Generally speaking it doesn't cause any problems - occasionally I spend the first 25 minutes of films wondering who is who and what's going on, and having missed the opening of The Departed I watched most of the film thinking Matt Damon and Mark Wahlberg were the same person.

However, there have also been some excruciatingly embarrassing situations where I've re-introduced myself (or ignored) people I actually know, although typically I've only met them a couple of times. Bizarrely, I'm worst with caucasian blonde women.