Great responses everyone

although considering the kind of folk here, it's no surprise that the views here are quite liberal.
I remember having a brief conversation with a friend of mine a couple of years ago. She is a tad liberal but generally a good Catholic and while she seemed ok with the thought of her bf watching porn and masturbating, she seemed to think that these things would stop once they are married. I hope she is not in for a rude awakening

Any way it would be rude if I didn't answer my own questions!
How many people in relationships masturbate? (I'm thinking quite a few Grin)
I wouldn't be called the great Sir Wankalot if I didn't

Would you be upset if your partner masturbated?
No. I'm sure he does, though I haven't ever caught him in the act yet

Of those who masturbate, do you fantasize about your partner or someone else?
Both. I think most of my fantasies involve nameless, faceless people. There are a couple of folk I've come across IRL that have made their way in though

Would you be upset if you knew your partner masturbates while fantasizing about someone else?
No. I don't really want to know the details though

I know he has a thing for tall, leggy blondes but it doesn't bother me. He still has a poster of Seven of 9 up by his desk. I wonder how many times he's jerked off to that

And what about fantasizing about someone else while having sex with your partner? - is that the ultimate taboo? Grin
I can't multi-task very well so no. I'm usually focused on what's happening.
Is fantasizing about an (unattainable) celebrity less "bad" than say the sexy neighbour or colleague?
No, not really - although if they ALWAYS fantasized about the real person, then maybe it's time to re-evaluate things? But then since these are all part of the thoughts of a person, it's not something I would be aware of any way so I guess it doesn't matter in the end.
I think it would be great to be in an open relationship that was based on trust and honesty. Not sure if I would ever get jealous or not.