If you can't think of ways Pinterest can make money then you simply lack creativity.
There are plenty.
There are plenty.
There are a LOT of people using Pinterest, and a LOT of Amazon products on pinterest.
1) The assumption is that the affiliate link model and market will scale to the size of Pinterest's eventual traffic maximums, that's a big assumption.
2) The assumption is that Amazon will want to allow Pinterest to suck profit out the door at that scale, instead of Amazon competing with Pinterest in one form or another instead, just like they're now competing with Groupon / Living Social (despite an investment in LS).
3) Amazon has a very long history of directly competing with companies that touch their platform.
That's an extraordinarily shaky business model to say the least.
I'm sure if I can't think of ways that Twitter and Tumblr can make outsized profits from their massive respective user bases, then I'm not being creative either. Oh snap, some of the best business minds are already on the problem and they can't figure it out either.
The same holds true for Pinterest, they're stuck in the same monetization box, and they're not going to suddenly show massive profitability either. It's blatantly obvious that platform will never monetize to the scale of their traffic.