Wow, these are exactly the same spots I have, in EXACTLY the same positions.
My best guess is that they come from some "parts" located in that particular area in the phone body. Could be the heating issue, but regardless, it seems that these spots are a common problem.

Frankly, although I wouldn't get bothered by these spots too much (true, they are apparent not that often, aka white screen), but given that the price paid was $514.54 last May (2010), the device is expected to be flawless.

By the way, do I read the n900 price on Amazon today (feb 26,2011) correctly ($349.00 )?
..Quite a drop in price, I feel stupid