I think it was proven to have no effect. It was always go down, and it will spin if the design of the bowl and the flow of the water (including the direction of source) induces swirl.
Try it at home (and I haven't so I may be wrong). Turn on your hot tap and note the direction the water goes down the drain. Then turn on the cold tap and note it's direction. Then fill up the sink, and leave the water for about half an hour to FULLY settle. Then let it go down being very careful not to instill turbulence with the plug.
It will choose a direction to swirl in because of dirt on the sink, flow remaining in the water, slight disturbences from pulling the plug. Use a finger and reverse the flow swirl direction - it will stay in the new direction. If enough LFSer's do this, in as scientific conditions as possible, from all over the world, then we can come up with a definitive scientific paper...