I think we've been subjected to so many tv partnerships that have had on-the-fence-chemistry (Bones, Castle, Law and Order: SVU) we are used to waiting for any real romance to happen just as the show is about to be cancelled.
But finally! An admittance of actual affection. Pinch me! Truth be told, I don't really love Mary with Marshall. However, the guy is too cute not to have some sort of love story arc thrown his way.