I know there was an article about a man who had donated to about 30 lesbian couples in Adelaide and there was some concern about it. However, the families all knew who the donor was and would apparently make this known to the children (at the right time). I think there is more of an issue if the donor is unidentified and you don't know how many other times he has donated. In the older sperm bank scenarios donors could donate multiple times and they wouldn't know how many times their donations had been used or how many babies had been successfully conceived. IMO this is a more worrying scenario as there is much more of an unknown element.

I think if you know the donor and you are aware of his history of donations and you are transparent about this with any children then I think you are doing the most that you can do.