I do not allow my students to tattle. If I did, I would never get anything accomplished. When a child comes up to me and starts to point fingers, I simply say "I don't listen to tattling." I usually back this up with, you need to try to come up with a solution to this problem yourself. By listening to the tattling we are not allowing our children to learn about dealing with uncomfortable situations, standing up for themselves appropriately, and in the end-gaining self-esteem.
There is one exception...I do have table tattlers. These students are experts in the art of tattling and I use it to my advantage when I lay out certain materials. For example: if I put out an ice cube tray filled with freshly squeezed paint colors, chances are by the end of class it will come back to me all mixed up and messed up. Rather than being able to keep it for the next class, I have to throw out a lot of paint, clean the trays and refill. So I tell my tattlers to keep their eye out for kids who mix the paint colors together in the trays, and if you see it, let me know. I will have them stop painting, clean up, and put their heads down for the rest of the period. I make sure I say this in front of the whole table. Since I've done this, no more paint mixing has been reported!