Been through 4 DSLites today...
Bought a Black one last week here in Gibraltar (British colony, but attached to the south of Spain) .. noticed a weird grey bit on the top screen yesterday, it looked like a bit of dust. Took it back today and the fun began...
The shop I got it from was one of those "you buy, I tell you what, me make special deal, you buy" sort of places, there isn't much choice in Gib, so I was surprised when the guy instantly went and got me a new one. I opened it up before leaving to check it, same problem (that and there was a massive finger print on the screen, new my arse), so I had to take a white one instead which seemed fine. Got that one home, popped Mario and Luigi in it... 2 green stuck pixels. Went back to the shop again and got told "this last exchange, no more" and this one even though it was it a white one seemed perfect. Then I went off and bought Animal Crossing (Ain't got a DS flash cart yet), and noticed a pin prick sized white spot on the bottom screen when it has the black background at the Nintendo logo bit of the intro.
I'm not sure what to do now .. I could take it back again tomorrow and try to get my money back or an another one, send it back to Nintendo (Still waiting for Nintendo to get back to me if the service centre in England will take it, It'd get back quicker if it went to Spain though), or just hope it goes away.. it's not really that noticeable.. there again I only bought the original one a week ago.
I'm leaving the intro to Mario and Luigi running for a bit to see if it shifts it. Fingers crossed