Less of a network effect than Facebook, I would think, because most users of Pinterest are pure content consumers, rather than hybrid content producers/consumers.

That said, they have a very large library of existing content, a large number of producers who have devoted a fairly large amount of time to Pinterest, and also... a space in which it would be hard to distinguish yourself by pure feature competition. How do you make a website that is substantially better than Pinterest at showing pictures and letting people bookmark them? If you create incrementally better search/recommendation technology, I think it would be hard to communicate your tech advantage to the average user, particularly before you develop a deep content library.

Delicious never acquired a truly mass audience, they never got out of the niche of traditional bookmarks as far as their peak audience days were concerned.

I'd say Pinterest has a few strong things in its favor: 1) it benefits from network effects, beyond anything Delicious saw; 2) people accumulate value in their use of the site, to leave is to abandon that effort; 3) they have a national (early global) brand, whereas most people never heard of Delicious 4) they dominate a demographic that is extremely valuable in line with their monetization plans, Delicious had nothing like it 5) Delicious was founded in 2003, the Pinterest scale potential in 2015 is drastically larger, with mobile opening a global audience of a billion potential users

It's also worth noting that bookmarked web sites rot, disappear, etc. Being able to visually go back and look at concepts, ideas, inspiration - is far more useful over the long haul (eg after three years of content accumulation as a user).

That's always a possibility, but I think at this point it would be just as hard to dethrone Pinterest. A lot of the content on Pinterest is pinned from within the site itself. I dunno what the percentage is, but most people I see that use Pinterest are usually just browsing their feed which is made up of pins from the people they follow (and the topics they are interested in). You also have to consider the amount of time that people invest into creating their boards and organizing all of their content. My sister has somewhere close to 20,000 pins now organized into very specific boards. She also has hundreds of followers and follows a ton of people.

They have some decent network effects. People follow each other and there are curated boards that are almost sub-brands on their own.

There have been some fairly well funded attempts to build a competitor (eg, Fab at one point tried it), but nothing really got close.

It's probably not as sticky as Facebook, but OTOH there's a lot more purchase intent.