I watched the movie for the 6th time today. I thought it was especially touching how at the end when Spock's told he can be beamed down to Khan's location he looks to Uhura to see what her response is to him heading into that possibly deadly situation. Of course he's not asking permission, but he's saying "I know this effects you". And she gives him her blessing because she knows he cares. It's this subtlety that makes me so happy with the relationship.