If you always hold the HTC EVO 4G in your hand while interacting with the touchscreen, then you're probably incredibly pleased with its responsiveness and accuracy.
But have you ever tried to lay the EVO on a flat surface (not your leg) and pull down the notification shade or just touch the top half of the screen without touching any other part of the phone?
Try it now.
Did your EVO's screen suddenly stop responding to your touch? If so, then touch any side of the device and try it again. Now it works flawlessly, right?
Unfortunately, it looks like some EVOs left the factory with improperly grounded touchscreens. So you're not alone if you can replicate the behavior described above. The anomaly has been confirmed by multiple users who have experienced this issue on various surfaces on more than one EVO, regardless of whether a case or screen protector is used. There are conflicting reports about whether HTC knew about this before the EVO was released, but the company does seem to be aware of it now.
An improperly grounded touchscreen is something that HTC Incredible users have also experienced, so there's no telling how or when this could be fixed for the EVO.
Note that not every EVO is affected by this. I tested mine (without a case) on a leather couch, glass table, cardboard, napkin, newspaper, and carpet and have seen no difference in responsiveness. How is your EVO's screen?