Scroll any number of Android forums, and there seems to be a fair few HTC EVO 4G screens separating from the device. It's surprising news as HTC's build quality tends to be exemplary, but you just can't ignore these stories.
By the sounds of it, the EVO 4Gs are perfectly fine until a few days' usage, with forum-poster Roman G writing "the funny thing is I did not noticed the light leakage either until today, but I did notice that the bottom of the screen was not near as recessed as the top of the screen," with other posters then confirming it took a few days for the screen to literally peel away on theirs too.
Also writing on AndroidForums, TheFoodMan52 said "If I push really hard straight down on the bottom corners of the screen, I can see it move about a half a millimeter down to where it's just beastly recessed under the border. Feels bad man. No light leaking though." While that particular poster doesn't seem to be having problems with light leakage, plenty more have posted saying they've noticed problems with it - with some already returning their phones for new ones.
Time will tell as to whether Sprint or HTC will confirm the issue, but in the meantime I'd suggest returning yours if you have noticed problems. Don't put up with inferior phones - even if it is the first-ever 4G one. [Android Forums via Engadget via AndroidAndMe]
Video below from forum-poster Roman G, showing how resistant the screen quality is - but also, how the screen peels away from the phone (at about 2:20 into the video), so much so that he can slide a fingernail in.