1) Why you'd want to consider a screen protector (or the risks of going bare):
It's fairly well known that the Evo 3D will be using Corning Gorilla Glass, and I'm sure many of you have seen videos where people have hammered away at Gorilla Glass screens with pens and rubbed all manner of keys, razor blades, etc. against them. But, the videos are worthless.
Gorilla Glass is great and is an improvement over other glass, tempered or otherwise in terms of strength and scratch resistance, but it is not the be-all end-all to scratch problems and many, many, many Gorilla Glass devices have been known to be scratched.
Why?
If you recall from grade school Earth Science, glass is known to have a hardness of anywhere from ~5.5-7ish on the Mohs scale of mineral hardness (which is a scratch test ranking of minerals). Let's assume that Gorilla Glass, because of its improved temper process, is at the far end of that scale -- 7 to 7.5. This means that Gorilla Glass will be scratch proof to most soft metals (iron, copper, nickel, lead, gold, and most types of unhardened steel), plastic, and harsh language. So your keys, razor blades, and paper clips are likely not to scratch the screen.
This however does not comprise the entire universe of things that will come into contact with the screen. What commonly occurring substance will still scratch the screen with ease? SAND. Sand is made of small bits of silica minerals like quartz, and small grains of other hard minnerals, all of which with hardness of 7 and up. These will easily scratch the screen with the slightest bit of effort. Furthermore, it's not unusual for sand and other debris to be caught in the pockets of jeans during the stone washing process (I know I've had to wash jeans with the pockets inside out several times to rid some of them of all the grit and sand), and just stuffing a bare phone into a jeans pocket and subject it to scratching risk.
The videos are fairly silly because I'm fairly confident that with your average glass -- say a window pane, windshield, etc., these things would effectively resist scratching by keys, razor blades, plastic pens, etc. just as well as Gorilla Glass. (Also note that the impact part of it is silly -- how "hard" you try to scratch a surface really plays no role in whether you can or not). When our keys would scratch something, like our older ipods or older cell phones, it's because the screens they used were made of plastic, which is extremely soft -- maybe 3 or 4 at best on the Mohs scale.
Now that most if not all large touchscreen devices have switched to glass in general (the Palm Pre was the last major touchscreen device I know of to use plastic), there is already a significant improvement in scratch resistance, and Gorilla Glass adds a bit more.
Screen protectors are certainly a matter of personal preference, and with Gorilla Glass, we've come a far way in terms of scratch resistance -- enough such that I don't think it's reckless to go without a screen protector. However, it's a matter of managing risk, because there is still a risk your screen can get scratched. At least for me, I'd rather replace a screen protector than an entire screen or worse, live with an imperfection on the screen itself for the lifetime of the device.
