Open Question: What's the impact of Reader's shutdown on traffic?

Let's say that there are only 1 million Google Reader users. In three days, that's a million people who won't be clicking on American Apparel ads. Which could directly effect the bottom line of websites that are entirely funded by ads, like blogs.

Is there anyway to know by how much though? What do you think the leading indicators might be?

I have enabled comments for this post so let me know if you have any answers.

On a side note, take a look at this alexa graph of I site like that has to be impacted by a Google Reader shutdown, right? Alexa Traffic Graph