It should be stored in a way that it can be used over and over again. By following the steps of the Six-Point Program it explains this process. The best way is to cover the top of the paint can with a layer of plastic wrap, then firmly seal the lid of the can over that. Once the lid is secure, then the can should be turned upside down. It really depends on the community but there are no national efforts in effect.
Some communities do organize paint swaps, collections or exchanges though.
Once again, the PaintInfo.org web site offers a nice guide that can help communities with leftover paint. The proper way to let small amounts of latex paint air dry is to put the open can someplace, preferably outside with good ventilation and where children and pets can not get to it. The best way to encourage this process with more than small amounts is to pour the paint into a box with shredded newspaper or cat box litter to absorb the water from the paint. Once the cans are dry and empty they can be recycled with regular recycling because most are made of steel. With oil-based paint it must be taken to a collection facility for proper disposal.