I had an Otterbox on my Hero, and loved it.
Doubt I will get it for the evo, especially if it covers the bottom buttons like on the HD2.
Also, the Otterbox Commuter case DOES cover the corners. It is basically a silicone case that is then covered with a plastic case. I dropped my Hero the other day, it landed flat on it's back from about 5 feet up. Made a loud noise from the plastic hitting the concrete, but when I looked at the phone, not a single scratch or anything. Oh, and the person I was talking to barely heard it hit the concrete.
These cases are rugged. Well worth the money, but I may try a Seido.