My mum's best friend is a fairly high profile actress (I'm not saying her name though!) and she worked with Alan Davies a while back. He's a weird crush of mine and I was incredibly disappointed to learn that he was aloof, self obsessed and not even remotely like he is on QI. Apparently the make-up girls hated him, which is a good way of telling who is nice and who is not.
She's worked with a range of Hollywood actresses too, of which Nicole Kidman was very stuck up, wouldn't acknowledge the other actors and spent the whole time in her trailer.
However Julia Roberts and Kate Winslet were very nice apparently