Like Reddit, it's a place to waste endless amounts of time. My girlfriend has gotten a little addicted to Pintrest and has since apologized to me for being mad that I sometimes getting sucked into Reddit on my phone.
However, the beautiful design is tuned for the target audience. I've watched several girls surf Pintrest and they use it very differently than most anyone I know who uses Reddit. Just the way they scan visually and randomly for something that catches their eye, rather than reading down a row or column and scanning for blue links.
All that said, I believe that the female audience will prove much more monetizable than Reddit's. For one, all pins already have a photo, so sponsored pins will fit right in with the flow. Secondly, the types of things people are sharing and looking at on Pintrest are extremely gift and "spoil yourself" centric.
Best of luck to the Pintrest team. Seems like they've got a great run ahead of them!