I always love to bond with my Pokemon. It makes me feel happy, and it makes the game so much funner when you know your Pokemon trusts you and loves you. But does it really make it easier to win battles if your Pokemon loves you? I'm not talking about return.
Thanks! ;D
A new battle mechanism that allows your Pokémon to become even more powerful when the bonds you share grow stronger.-This site or Junichi Masuda blog
So it is possible in the new X and Y games, but not from any of the previous games.
No, it doesn't except in the anime. :/ EVs, IVs, and stuff like that determine strength. But we all have an inner strength. :)