My personal opinion is this: when someone says I love you it conveys a certain level of affection that goes above general feeling. I love my children, I love my best friends, I love my family etc. When someone says they are "in love" with someone it usually conveys a different level of the love sentiment, one that wishes to be "with" that person in a physically intimate companion sort of way. Boyfriends and girlfriends claim to be "in love", husbands and wives or significant others claim to be "in love" with their mate, so I have just always reserved that sentiment and understood that sentiment to be one that carries more conditions and expectations than the other. My love for my children is unconditional (I can't imagine ever NOT loving them) whereas my feelings of being in love with a mate carries expectations of reciprocity and "please don't hurt me or disappoint me" kinds of twinges. You see what I mean....the expectations are just different. I was "in love" with my ex at one time, and he hurt me very badly. Do I still love him, no, nor am I "in love" with him. My children have done things that hurt my feelings, but do I still love them, yes of course.
I know the phrase "I love you but I'm just not IN Love with you" seems like such a cliche, and a bad one at that, but I think it has merit and I do think there is a difference when you truly examine what the person is trying to say. This phrase doesn't come out of the mouths of friends, family, or our children, it comes from boyfriends and girlfriends, spouses, significant others and such, which would indicate there is indeed a difference in the terms.
coco