Curling is a fascinating sport and I was sent this link (I forget by whom) that says that the way the stone veers as it moves along is a bit of a puzzle for physicists. (If the embedded video below does not work, follow the above link.)
I would be wary of the friction-caused melting theory because as I said in a previous post about why ice is slippery, that explanation is not tenable. I had not been aware that the ice surface in curling are prepared is such a way as to produce tiny bumps on the surface of the ice. I suspect that that it the most probable cause for the unusual behavior, though the precise mechanism is not clear.
The problem about the “pebble theory” seem that I have seen curlers on natural ice surfaces (indoors) that I am reasonably sure did not receive any spraying and nicking. People skated, played hockey and curled, all on the same ice surface.
Does that mean that in those circumstances the rock curled the other way? It was a long time ago and I never noticed which way the stone curled. Personally, I blame it on the bloody-minded Scots.
jrkrideau @1: The bloody-minded Swedes claimed to have solved it a few years ago. Seems its the roughness of the stone’s contact surface rather than (or as well as?) the ice’s pebbling.
David Attenborough’s look at curling is also worthwhile: