Did you know that different kinds of erasers exist for different purposes? Or that one might work better than another?
From Pencil Talk: Erasers: The Pink Pearl, the Staedtler Mars plastic, and others
From A Penchant for Paper: The Great Eraser Review: Pentel Hi-Polymer, Staedtler Mars Plastic, and Staples Brand Erasers
From Toad Hollow Studio: The Best Erasers for Graphite Pencil Drawing
From Lung Sketching Scrolls: The Pencil Eraser Comparison Review that never Was
From About.Com Chemistry: How Do Pencil Erasers Work?