Leftover paint can go one of two ways... If your paint cans could choose they'd choose to be donated to Community RePaint (via your Household Waste Recycling Centre) rather than being forgotten in your cupboard and getting stiff and old!
Decided that colour wasn't quite right for your kitchen after all? Only needed one coat of paint so ended up with plenty spare? The paint you no longer need doesn't have to end up in landfill.