negotiating with debt collectors? Anyone with any experience in this?

I had literally no idea that you could do this until Cracked.com mentioned that this a thing that people can do. I had never considered that as a possibility because debt collectors are scary and I'm easily scared. And because of the way shopping is now, is that you assume that the cost is what the cost is and there's no negotiating with say Wal-Mart.

Is it worth it to try? Has anyone had any success here?