I will drop my iPhone 4 a lot. I've dropped each of my iPhones numerous times, but never resulting in any significant damage beyond some minor nicks, scratches or dents. I've owned cases, but eventually end up going naked--and usually the drops occur when it is naked (or so it seems).
I may go screen protector, but I don't want one that will degrade the screen quality.
I have Safeware warranty on it. Costs me $99 or so. Get $500-$50 deductible in event of loss, theft, or accidental damage. A case would be at least $30. Eventually I'd want a different one in a year--adding to at least $60. Forego the screen protector and I'm saving a total of $75 or so. That's my plan anyways--not full proof, but it is just a phone, albeit a really expensive one without subsidy.
I just remembered that $450 would not cover the full price of a new 32GB, so probably no savings if loss. But worth the advantages of nudity and peace of mind.