I love looking at the amazon top 100 sales.  What I was wondering is if this, which is a sample, could be used to predict NPD in some ways.

You dont get a quantity of course, just a ranking, so it seems in general you couldn't predict unit sales (though, maybe you could make some headway in that direction eventually). But it seems you could try predicting relative sales. By this I mean, whether PS3 outsold 360, or vice versa. You would of course have to correlate amazon to NPD. By this I mean it seems PS3 always outsells 360 at amazon, but this isn't the case at NPD. So of course you wouldn't be looking at absolute strength but relative strength.

You also have to allow for multiple sku's in the top 100, but I have already figured out some methods to deal with that. 

What you would need to do is check the rankings at set, consistent intervals. Lets say, check every tuesday and friday at 4pm and record your findings. Or however you want to do it, you could try different things. 

Anyways, I was thinking of doing this, maybe one of you would like to also or instead. 

Amazon really isn't indicative of general sales because Amazon runs a lot of site-specific sales and stocks a lot of games (rock band, ddr) that retailers don't have a lot of because of space limitations.

I'm just talking about the consoles, though. Hardware sales. And current hardware is almost never (if ever) discounted. I dont really care about software. Hell really I just care about PS3 versus 360 I dont even care about wii or the handhelds.