Comfort, utility, and protection
I am not a clumsy person, but I once dropped my Treo phone in the parking lot and was really bump. On the other hand it doesn't make sense to cover up the feature that you try to protect because you can't enjoy it: thinness, elegant design, etc.
But then the most important part of the phone is the screen. I really like the feel of the glass so I don't use a screen protector. When it comes to putting the phone down, with a case that has a slightly raised edge for the screen, I feel comfortable putting the thing face down, otherwise I end up putting the phone face up and subject the screen to other danger. So a case makes sense here.
Then there is the comfort factor. I found the iP4 not comfortable to hold without a case. The iP5 is better because it is lighter, but I would prefer it a bit rounder on the edges. It is a bit tricky to pick up off a flat surface like a table. A less slippery case would help here. Also, while I love the thinness of the iP5, I wonder if it would actually be more comfortable to hold had it been a bit thicker. Mind you when it lies flat in your hand the thickness of the phone doesn't matter. But when you tilt it beyond 45 degree or worse yet vertical as when making a phone call, it feels almost too thin. It's just simple physics: trying to apply force or the thin edges of the phone to overcome gravity. A less slippery case that increases the thickness helps here.
I love the look of the iP5, and the light weight makes it a lot more comfortable to use without the case than a iP4. I am tempted. But I think a case will make it more comfortable to handle. It's a trade off between function and look. But if the screen is the most important part, as long as the case doesn't affect the screen (edge reach), I think I am leaning toward a case.
