I have no screen protector on my Incredible. I put one on when I first got it, but the screen is so much nicer without one. Plus, I suck at putting on screen protectors.
I keep the phone in a Nexus One sleeve in my pocket and my phone is in perfect condition, can't find a scratch on the screen at all.
That's what I did with my Desire, I got the "genuine" HTC case with a pull tab to extract the phone. But now I'm concerned that the constant insertion and extraction of the phone itself will wear out the conductive layer of the touch screen... On the plus side, the way the screen rubs against the inside of the case actually helps clean fingerprints from it...
When I tap the screen on my HTC Desire with my fingernail, it feels and sounds like cheap plastic. Not at all confident that it would last any kind of punishment.
Can't see the point of body armor without screen protectors, like the expensive silicone covers you can get that you just snap to the back of the phone. I mean, you can even order back covers for HTC phones from their website for the same price as one of those "protectors"'. The screen is what needs protection as far as I'm concerned, not the back cover. I've never dropped a phone in my life so far, and don't intend to.
This is what my Samsung flip phone looked like after 4 years of use. I always kept it on a dedicated "phone pocket" with no other items. Now imagine if that was the screen instead of the back cover...