My hubby said it first. I think it was in the first month of our dating.
Made me very uncomfortable because I was a wee bit different about my emotions back then :) I thought he was too young and didn't mean it (him 23, me 27)
We've been together since 89, and now that I see how precious the people we like and love are -- lost a lot of good friends/family in the very recent years -- I tell people what they mean to me, with words or gestures depending on what they feel most comfortable with.
Of course, I smother my son with I LOVE YOUs all the time, whether he's comfortable with it or not, but hey! he's only 3..what can he do! lol