I've dropped my iPhone a few times, not too far from the ground mind you, but enough for the bumper to actually protect it. It's not a complete waste of money. I chose the bumper initially for the following reasons: 1) I trusted Apple in its own design, that it would make bumpers fully capable of protecting their own products. 2) Aesthetics: i loved the clean look of the bumper which didn't hide the sleek design i oh-so love. 3) Ease: it was easy enough not to search a bazillion websites (which i had already done) to look for the perfect cover for my ~$700 MSRP investment.
One thing i have discovered and tested for myself: the iPhone 4 without the bumper gets better cell & data connection than with the bumper on. Without the cover i notice significant improvement of battery life and connectivity, so much that i leave it off all the time. Sure, i was initially paranoid of exposing such beauty to damage, but after a year now i leave the bumper off. Without the mostly useless bumper, I get to show off the design and do not have to deal with performance issues anymore. If you have a bumper, take it off. The iPhone 4 is best when it is bare.
iPhone 4 bumper review- Summary:
Cons: Scratches brushed metal antenna, hinders connectivity, strains battery life.