In the seven years its been running, Planet Ark has recycled 10 million printer ink cartridges. That's about 4700 tonnes of waste that didn't go straight to landfill. That's a pretty good effort, but I reckon we can do better.
Because of the plastics and metals in printer cartridges, they take a long time to break down in landfill. But they can be relatively easily recycled, either being reused by printer manufacturers or recycled into new products.
To find the nearest place to recycle your cartridges, point your browser at cartridges.planetark.org. It may take a little bit of extra effort, but it has a real benefit for the environment, so you should do it anyway.