It is still visible straight on but it is does get significantly darker as I tilt the screen as you pointed out. Also it is more visible on white websites like maemo.org which is what I used in the picture hoping the poor quality cell phone camera would pick it up.

The 2 spots developed when I started carrying the 770 around without the hard cover in place. I guess for now I'll assume the dark spots are attributed to vskin3's explanation of unequal distribution of light from the LEDs. I hope to come across more information on how to fix this problem. (if it's repairable)