Personally, I have a problem with Clark even having (penis in vagina) sex with any human without telling her the truth, because there is a risk of pregnancy (no matter how slight) and a woman deserves to know if she's running the risk of pregnancy-by-alien. The potential consequences are too huge. Obviously, this problem does not exist in any version where Clark knows he is incapable of reproducing with a human.
Well, on the plus side for L&C Clark, he did not have sex with Lois before telling her. I guess we can technically say that about the Superman II version of Superman, although this rule also means he should not do the memory wipe kiss.
My biggest issue is, what if Superman has been told he can not have children with a woman, and he has sex, and then she gets pregnant because the calculations were wrong. This is at least one of the background conditions in some versions of Superman Returns fan fic.
