I just noticed this today. I know a few people have mentioned having this problem on kindle boards so I thought I'd really give my screen a thorough look over before the 30 days is up to see if I had anything like it. Ha, bad idea.
At first I saw nothing at all, but then happen to come across it tonight. I had the light on high and reset my kindle and saw it on the start up tree screen in the dark area. I'd have probably never noticed it, but as it was starting I scanned the screen again. I can really only see it when the light is on high, say 20 or above, and it's very tiny. I don't see it when reading at all, but when I turn the page and have the light up high sometimes I'll notice it now because I know where it is.
My screen is fine otherwise so I'm not sure 100% sure I'll exchange it, but it again goes to show how bad the quality control is on these. Anyone else notice this on theirs? Although I wouldn't suggest looking too hard. LOL.