Which shareholder? The guy in it for the long haul or the guy looking to flip the stock in a quarter. If Bezos had maxed profits on selling books, the market cap might have been the same as Borders at its peak. The key question is whether the projects are positive on some npv basis. Given bezo's track record, I see no reason to believe otherwise. Short term shareholders might disagree though.
I think you should make plurchase completely public, so that I can see everyone (and they can see me). That way, I don't have to invite my friends to shop + I can spy on other people (making it fun even when none of my friends are online).