I tried my best but it's almost impossible to photograph. But it's there. The grid looks like a foggyness that falls somewhere between condensation, dust, and fingerprint smudges. Watch the video and you'll see the grid. it will only show up when the light is reflecting at certain angles.
I've also done some digging, and I can confirm that I'm not the only one to see it. I've found a bunch of comments about it here and here, and I even found it discussed on the official Asus Transformer support forums. Much to my surprise, I appear to be the only one bothered by it. No one offered a solution for the problem other than wiping the screen (that didn't help).
It's going back to the store. I love this tablet, and it's truly awesome. But I'm not going to put up with an obvious screen defect on a $400 tablet.
Here's the video. I think you might want to click through and watch it in higher resolution on Youtube.