Vertical markets for social networking sites

Goodreads is a social networking site for book lovers. That really puzzled and surprised me. I know for a fact that vertical (niche) markets are always better to start off with when you're starting out. It lets you build a community of like-minded people, and it makes you focus your product, which makes it not only easier to build, but makes you design a tighter product.

But the question to me at first impression was, why would people join a vertical market for something that already exists?

Goodreads is a well designed site. It has a core, limited feature, and it's clean, and it's easy to add books that you've read and write reviews on them. One can also see what your friends are reading and what they'd recommend.

However, the big three social networking sites, Friendster, MySpace, and Facebook all have a section where one can list and name books that interest you. And Amazon, already has both places to read/write reviews for each book, and a recommendation system that works pretty well. In addition, you can actually buy books there.

So what does Goodreads have to offer? Well, for one, at this early stage, it's fast and responsive, and the mechanisms for actually adding a book is very easy. In addition, it plays on one of the elements of gaming, which is namely, collecting. And that goes along very well with those that read books...they like to have a full bookshelf (almost like trophies on display). There are many games that focus on the collection aspect. Yugi Oh! and Pokemon are the two that spring to mind. Goodreads is like pokemon...for people that like to read.

In addition, I think the book covers help enforce that idea of a collection, so you can see books in your bookshelf. And not only that, you can segment them according to what you've read, are currently reading, didn't finish, etc. That's something you can't do with a normal bookshelf.

I won't say that it's inevitable that a niche market in an already saturated global market of social networks is going to succeed. But the way Goodreads did it makes sense. In fact, the same mechanism of collection that I outlined above can readily be applied to a social network of fashion geeks.

I own this shirt, or that blouse. I can see what my friends are wearing the next day. I can ask to trade clothes. I can make outfits for myself from my closet, and recommend them to others that have the same pieces of clothing. I can rate clothes and brands, and I can see what the overall trend for different types of clothing are.

I'd be tempted to make it myself, since I usually have an awful time shopping for clothes--I can never remember what I already have. However, 1) I'm not much of a clothes person myself, so I'll only probably work on the 'help me choose my clothes' part, and 2) there are already plenty of niche market fashion sites out there.

What other vertical markets for social networks do you see that would have potential?