I am curious as to what different people take this to mean here is my own definition please comment with yours.

The words "I love you" mean so much. First off it means that you want the person your telling that to, to be happy, even above yourself. It means that when your around them you somehow feel like everything is going to be ok, even if you don't always know what to do, which you won't. Welcome to human existence. It means that they are worth whatever pain in the ass that you go through on their behalf, and it means you want them to live the most fulfilling meaningful life that they can. It also means that you want to be their the whole way.
Now, when they say I love you in return, that opens even more meanings, as now that you have acknowledged such and that it is mutual these words become a promise. A pledge to each other that states, you want to be with the other, and a promise, to try to be happy. If they love you, that is what they want... they want your happiness, and if you love them, you want theres. The thing is though that we have such very little control over the other person, and love is most certainly not controlling. We want them to be happy, and yet we don't always know what to do, or sometimes we forget and stumble. Love forgives, it has to in order to survive. We don't always understand it but when we love someone we love them.

EDIT: In light of what has been said I realize that I did not ask my question clearly enough, I'm looking at more the relationship love. It is because its hard to say without meaning it that this type of "I love you" fascinates me.