Missed a couple big ones from companies they mentioned. Yelp paid professional reviewers to seed cities they wanted to establish themselves in. To my knowledge they were honest reviews, but people were still put off by it.

And the Airbnb spam debacle was left out as well. (http://davegooden.com/2011/05/how-airbnb-became-a-billion-do...)

For the record, I use both services frequently, but those are notable omissions.

Really curious how much PayPal dumped into buying eBay items. Doesn't seem like something you could do for long, so I imagine it had to be highly targeted.