This offer is happening now through 1/31/12.
You will get double Coke Rewards points on any Coke Zero product (including Cherry Zero) and size.
I wish I had saved my points from Coke Zero products! :(
They do these promos every now and then for Coke Rewards but it's impossible to know which products they will do it for and we can't save them all and wait for a promo!