On last night's episode: In what reality would Claire have not sprayed Desmond with mace when he followed her into the elevator? In the Lost alternate reality, that's where! It was cool to see Sun recognize Locke in the AU, and that further confirms the bleed over between realities.
The Desmond on the island didn't appear to know that the Locke-ness monster wasn't really the John Locke we know and love, so I'm leaning a bit against the theory that he was actually trying to take Subsitute Teacher Locke! down with the car. I do think that he was trying to trigger a realization of the Island reality. The true love thing wouldn't work on Locke since he already had someone in the alternate reality... I do think that eventually, John Locke will have an epiphany-type experience in the hospital that will cause his consciousness/memories to touch base with the Locke-ness monster. Any guesses as to what will happen then?