An addendum to my previous post:
I ran into Jeff at work today, and he said "Hey, did I see you in Brooklyn last weekend?" Apparently he did, as Alex and I were walking to the Brooklyn Museum, though I didn't notice Jeff. So, chalk up another coincidence -- though, as usual, it's not totally out of the blue, since we both went to see an exhibition that closed this weekend.
Coincidentally, Jeff had been part of an impressive coincidence-within-coincidence that happened previously.