I don't know how the numbers work out for Kobo, but I really don't understand why we (as consumers) should jump in glee to be giant billboards.

Don't get me wrong: I think that giving reader the ability to share what they read with friends or discuss what they read with other readers is a great idea. But there is a huge distinction between that and being manipulated into being salesmen.

For what it's worth, I ran tcpdump on the Vox and there is an astounding flurry of network activity when the Kobo app is launched. One of these days I'm going to figure out exactly what the activity is sending. Until then, I'll stick to third party reading apps.