The ending + the idea of this movie
When Amy Adam's character lays her head on Theodore's shoulder at the end, I don't think that means they're going to start a relationship. I think that's actually just a "friendly/affectionate" gesture between two close friends who are almost like siblings. The same exact thing happens with me and my co-worker. She also does that sort of thing to me even though she has a boyfriend.
I think this movie is not about transhumanism, artificial intelligence or futurist technology, I think it's more about feminism and female empowerment. Women are gaining the upper hand over men. I also think in order for men to adopt to this new world - men have to become more female to a *certain extent*. One person in the film said Theodore seemed like a "feminine" man, that he was in touch with his female side.
Relationships and marriages are becoming harder to do in this current time, I think one has to be patient and poetic like Theodore to actually transcend these challenges. The relationship between Theodore and Samantha was not about sex at all, because Samantha was not physical. But it was a spiritual relationship based upon deep/engaging/thoughtful conversation.