gushiggins: I don't say anything about anything until the moment of truth is at hand. If they find out beforehand, fine, but she isn't getting a piece of me unless I know that she wants to make love with me, not my endowment.
That being said, if things are going in that direction, I always insist on giving oral beforehand, and make a point to tell her so. If she asks why, I say something to the effect of, "Well, one, because I love to, and two, the extra lubrication really helps." More often than not, that'll peak her interest, and I just go naturally from there.
I know that she wanted me for me, and she's not totally surprised/freaked out when she sees it for the first time. Win-win.
-Z