In San Francisco last week I got to meet Chris Dixon, a partner at Silicon Valley investment firm Andreessen Horowitz. Naturally I asked him about Pinterest, which everyone expects will file for a huge IPO in the coming months.

Andreessen Horowitz participated in a $225 million investment round for Pinterest, so if anyone might know what Pinterest's numbers look like, it would be an Andreessen partner. The round valued the company at $3.8 billion.

Dixon says that when it comes to monetization at Pinterest, people should think about Google rather than Facebook, in terms of how its e-commerce traffic performs. That suggests Pinterest's traffic is much more valuable--and that revenues will be much higher per user--than Facebook's is, in some scenarios. (Dixon didn't specifically say this, but as his quote below indicates, these are the benchmarks we're talking about.)

Dixon couldn't be drawn on a dollar amount for Pinterest's revenues--they're likely modest right now as the company has not yet launched its advertising application programming interface. (An API is the device that will allow advertisers to plug their own ads into Pinterest.)

But he did give us a clue as to how robust they might be. Pinterest likely offers a stronger ad environment than social media does, but not as strong as search advertising does, he says. 

The context here is that although Pinterest is obviously smaller than Facebook or Twitter as a social network, it dominates one specific niche: Online retail and shopping.

Pinterest delivers more traffic to retail sites than Reddit, YouTube and Twitter combined. Facebook still delivers more total traffic, but that's because of it sheer size. In terms of retail, Pinterest bats above its league. Here's what Pinterest's share of all referred web traffic looks like according toBusiness Insider Intelligence: