Pitting cherries can be time-consuming, even if you have a pitter, or use metal hairpins, paper clips, or chopsticks. Each method only handles one at a time. This method, from Sunset Magazine, preps a handful of cherries at once.
You can see how it works in the video above. All you need is a rubber or wooden mallet, and a sheet of baking paper. Spread out a bunch of cherries on a cutting board, and put the paper over them. Then tap the cherries with the mallet gently -- you don't want to crush them or smash them, but you do want to break them a litle bit. Make sure you get all of them, and then pull the paper back -- each cherry should be just split enough that you can pop the pits right out without having to cut the cherries or go digging for them.
Most of the other methods we've mentioned are better than this one if you want to keep the cherry whole, or in neat halves for salads, snacking, or some presentation where appearances count. If you're baking and will end up chopping or mashing the cherries anyway, this method works like a charm.
The Fastest Way to Pit Cherries [Sunset Magazine]