[quote=henrypotema]
Okay yeah you'd end up with long names, but surely feminists can agree that this is the only true equal thing to do?
[/quote]

Feminism would argue that it should always be the woman's last name, cause involving a mans at all is exercising a power fantasy over women and is Patriarchy. :hehe

In all seriousness though? Yea, that is essentially an equal thing to do.
Another method though could be:

1) Use both but separate. Two last names? Make one a middle name? etc.
2) Alternate last names per child (But this would probably confuse both outsiders and the children).
3) Just let the couple decide for themselves which last name to use.