I knew that my Dad was a sperm donor when he was younger. I can't remember ever being told, but i must have been at some stage. I never thought of kids produced from the sperm as my siblings, and still don't really. I have adopted siblings and they are my family, so i see those you grow up with more as more important.

Adoption was never kept a secret in our family, and i don't think donor egg/sperm should be either. I also think it is info that the child may want to keep a secret, so wouldn't feel the need to share with everyone.