My kids probably think I'm a miserable old bag most of the time, as I'm quite happy to tell them no and we can't afford it and you're too young for that etc etc. I would say we are reasonable, they probably wouldn't agree, but we try to let them do as much as we can afford without going into debt and be as flexible as we can in helping them accept as many social life offers as we can. However sometimes we just have to end up saying 'No sorry, you can't' - either because (occasionally) we have some social life of our own, or we can't afford it, or because one of them is already doing something that takes up our time.
I have a friend who seems incapable of saying no to anything her children want - material or activity wise - on the basis that she feels her childhood was deprived so they should be able to do everything they want. Maybe I'm the miserable one here but I do feel that we have to learn to give and take and to live in a family where everyone has equal rights, and the kids don't end up downright spoilt because no-one ever says no to them. I hope my kids will grow up as balanced and generous people who are polite, considerate and enthusiastic about life even if they lack the many experiences and material wealth of their friends.