I like Lois' thought process here. Marrying Super Clark is very different from marrying ordinary human Clark. I've always thought that it wasn't fair for Clark to propose without telling her (though it made quite a cliffhanger - I was antsy about it all summer that year). I understand his reluctance to tell anyone at all ever, but asking, "Will you marry me?" is really a false question when the "me" isn't who she thinks he is.

"It is a remarkable dichotomy. In many ways, Clark is the most human of us all. Then...he shoots fire from the skies, and it is difficult not to think of him as a god. And how fortunate we all are that it does not occur to him." -Batman (in Superman/Batman #3 by Jeph Loeb)