how much they give back, and how incredibly warming and satisfying it is :)
Some days are so busy and we don't have time to just snuggle, and then when I eventually, late in the evening, plonk myself down on the couch, they will come over and practically demand to be stroked etc, and will cover me with little licks and do that head-butting thing they do to show affection. And I am, every time, amazed at how social they are, how it seems to be so important to them that we do this every day.
It reinforces my belief that we are meant to live together :)