I think the overall theme is that we can create our own destinies or something like that. WALL-E's purpose was to clean up Earth, but he ditches all that to go after EVE. EVE's purpose was to bring evidence of Earth's inhabitability to the Captain of the Axiom, but she falls in love with WALL-E and decides to help him out instead, even though her programming urges her to complete her mission. The Captain sees a video of the president of a corporation saying that they should give up on the Earth, but refuses to believe that there's nothing left that can be done for the planet.
It sends the message of "please go green" without messing up the overall story (unlike Happy Feet, but that's my opinion). It's kinda scary though.... it points out that if we have too many luxuries for too long, we'll....uhhh.... kinda get FAT eek . Wow... Buddha was right eek (he said something along the lines of don't have too many luxuries) . Anyway, I recommend this movie to EVERYONE!!!

EVE and WALL-E forever!!!!!!!!! heart heart heart heart heart heart heart heart heart