My first year with it, bumper and belt case.
My second year with it, bumper case no longer mandatory.
Right now, we are in the honeymoon stages of it like with anything new and just want to coddle it like a baby. After a year or two, the cycle becomes wanting a new phone and taking of this one far less than the first few months.
I think the phone is beautiful and can completely understand going naked with it. I was inclined to buy a bumper to protect the sides and don't like the edges of the metal band. Not flush and feels jaggy. I also don't like the phone touching the surfaces, and the bumper provides a lip. I generally don't like cases because it makes it feel bigger and could trap dirt (or sand) which over time can ruin the phone. But the phone itself is a work of art and definitely makes every previous iPhone look and feel fat and cheap. This feels and looks like a $1000 phone, not a $600-700 without contract. The iPhone 4 looks like it fits with the fashionista/high-end niche market. iPhone 4 makes the Giorgio Armani phones from Samsung look like trash.