I don't have a Nexus 7 yet but I'm familiar with "dead" pixels since I've had to fix them on PSPs and even my LCD a couple of times.
There are lots of "dead" pixels, but let's just talk about two, the most common. You can have a dark pixel, which is dead and there's nothing you can do about it or you can have a stuck pixel, which is fixable, and I will explain how, but let me just tell you that sometimes a pixel looks black because of the colors around it and you lose all hope, but don't fall for that. If you want to check the color of the pixel to see if it is in fact dead, then just get a white image on the whole screen and see the color, if it is very dark then it is dead, but if it isn't, do this:
Download this video:
Click to view quoted video
make sure you download it and have it in MPEG4 and in 720p and play it on your tablet in full screen. Hope this helps