The userbase is 80% women, and the percentage of active users who are women is probably even greater. Not sure of the demographics of delicious, but I'd guess roughly the inverse.
Also, the fact that the userbase is mostly women is materially important in valuating the business, since female users are generally worth much more than male users.
IIRC in the US women drive about 80% of purchases, meaning each female user is worth several times what each male user is worth. In terms of communicating the value of the business to investors, the fact that the userbase is mostly female is arguably the most important aspect of the site.
I don't have a good cite, I believe it's supposedly all purchases though. Not sure how accurate it is, but my understanding is that sites with a lot of women do have vastly better clickthrough rates and conversion on their ads so it's not entirely apocryphal.
But I'd say Pinterest-style scrapbooking is a type of bookmarking, a visual style of bookmarking. And a lot of the things people get excited and interested in are at least in part visual: fashion, lifestyle goods, home and garden projects, wedding day stuff, arts and crafts, food and drink, cars etc.
I'm just looking at the comments on items on the Pinterest homepage: "Love this!", "WANT IT", "available now on Etsy", "Gift ideas", "can someone give me a link where i can buy it online". It's a veritable treasure trove of consumer information for people in the right markets. And it has just enough pictures of hot men, cute baby pictures and occasional silly memes to remain interesting.
Yes, it appeals more to women (and some gay men and arty types and so on), but in the right hands, it's a powerful tool for understanding and supplying the needs and wants of a significant market segment.
There's an interesting possibility for doing some kind of content partnership: imagine Pinterest TV, discussing all sorts of fashion and lifestyle stuff, with partnerships with existing media and retail brands - think Mumsnet or L'Oreal or Vogue or MTV...