If you designed the perfect little rectangle, would you bristle if companies started designing little form-interrupting gewgaws to slap onto it? I guess that's the price you pay for ubiquity. And you can't deny that some of these widgets add good functionality, like the Glif.
And while it looks a bit absurd, PhotoJojo's latest $35 iPhone add-on is a telephoto lens. It gives you 8x zoom, features a manual focus on the lens body, and comes with a stabilizing tripod.