Pinterest is a social image bookmarking service that became very popular in the last several months. It's a pinboard style website that allows users to share and manage images or videos (called pins) organized in boards. Often these images link to other websites (usually, to the location where the image has been taken from). Users can re-pin images from other pinboards, like pins or comment on them. Also users can follow some or all of other users boards. To make everything even more social, there is a possibility to share pins on Facebook and Twitter. All of this colorful service sounds quite attractive and it has proven to be as millions of users have joined the new service for the last year. Pinterest.com has proven to be especially popular among women with enormous amount of fashion or food related pins. Of course, business opportunities have not been overlooked by both Pinterest's owners and various other brands so, there are lots of pins linking to commercial websites. There is nothing wrong with that though.
The problem I see with Pinterest is its inclination to make the rich richer. What I mean is the following. When you pin an image or video on Pinterest there is not a section with the latest pins where everybody can see what you have just pinned. Practically your pins are visible only to the people who follow you and if you are a new user, most likely you won't have many followers. On the other hand, older users normally would have more followers so their pins are exposed to a broader audience. The chances to get new followers are practically coming from the exposure of your pins so people that already have more followers than newer users will continue to gain more and more just because the system is in favor of them and there is not an equal chance for everyone.
There are thematic sections where everyone's new pins could get into but there is some limitation based on time or amount of pins (I am not exactly sure) so only a fraction of your pins could actually get there. So it's possible the least attractive of your pins falls into these sections thus not drawing any interest to your boards. Again, this does not make everyone equal. The last option for exposure of your image or video on Pinterest is that it becomes popular. And of course, this is again much harder for new users cause pins of users with more followers get more re-pins and likes thus having considerably greater chance of getting into the "Popular" section.
Now some of these characteristics are pretty much the same on many other social bookmarking web sites. The difference though is that most of the other websites offer "New", "Latest" or similar section so every pin, story, link or whatever has a chance to be seen by everyone. This is not the case with Pinterest.
Frankly speaking, I am not sure how this could affect Pinterest's performance and growth in the future. My opinion is that some people could be put off cause even if the original idea of Pinterest has been to offer organization of images in the form of virtual pinboard, actually most of the people join online social services for getting exposure, connections, following or anything that could be labelled as a social activity. Offering a very limited chance for exposure to their new users, Pinterest owners limit the social element in their experience significantly. Whether this will be crucial for the future development of the site is something we are going to see but to me it looks like a case of an overlooked piece of functionality.