Are Smartphone Cases Really Necessary?

I've been carrying around a PDA or smartphone for well over ten years now, and I've almost never used a case.

I've had a long run of good luck -- I only ever broke the screen on one device in all this time, and to be honest, it was mainly self inflicted, as I was quite intoxicated when that disaster happened. 

But a recent mishap has caused me to reconsider this policy.  I broke the screen on a Dell Streak...and it wasn't doing anything all that extreme. I let it slip out of my pocket while I was walking up some stairs, and the device landed exactly wrong. The Gorilla Glass screen didn't break, but the LCD did.

I'm thinking that if I had the smartphone in a case, especially one of the ones from OtterBox, this wouldn't have happened.

On the other hand, cases add bulk, which is a hard thing for me to put up with on a device that I carry with me almost everywhere. And cases aren't cheap. A good one will set you back $30 or more.  

So I'm looking for your opinion: Is the extra protection of a case worth the extra expense and bulk? And I'm not talking theory here -- I want to know, do you keep your phone in a case at all times? Or part of the time? If so, what type of case? If not, why not?

Tragic (or funny) stories about how you broke your smartphone are welcome as well.

Chime in with your thoughts in the Brighthand forum.