Just wanted to pipe in that I'm running into the same problem as everyone else now. I've had the EVO for maybe two weeks. I was using a silicone case, but there was a ton of dust collecting on the edges so I just removed it, been leaving the phone bare. It's only in my pocket when I'm going from one place to the other (the rest of the time it's either being used, sitting out charging, or sitting out playing music). It's in the upper-left corner, under the htc logo, like everyone else.
Pretty shoddy, if you ask me. I love the EVO, it's a great phone in a sexy form-factor, but dust under the screen after two weeks is amateur hour, HTC. Hopefully it doesn't get worse...