According to Experian, Pinterest is the third most popular social network in the United States. So it’s no surprise that brands have flocked to set up shop, particularly given that Pinterest may be a far more profitable platform for brands than social networking stalwarts like Facebook and Twitter.

What’s remarkable about Pinterest’s rise is that up until yesterday, the social network was still technically in an invite-only beta. One of the reasons cited for this was the company’s desire to maintain cachet and a feeling of exclusivity. Others suggested that the startup was trying to mitigate scaling risks, which can easily put a dent in a promising startup’s plans.

Apparently, however, the Pinterest team believes it’s ready for prime time and on Thursday brought its social network out of beta. Now, those wanting to pin can join Pinterest sans invite using an email address or Twitter or Facebook account.

Open sesame: implications for brands

Despite Pinterest’s invite-only status, the social network had amassed impressive stats: more than 10m members and 100m unique visitors per month. As one might suspect, that was more than enough activity to turn Pinterest into a prominent source of referral traffic for some retailers.

Now that Pinterest is open to all comers, brands using the image-centric social network can almost certainly bank on Pinterest growing its member and unique visitor figures even more rapidly. But what does that mean? Questions raised by Pinterest’s exit from beta include:

  • Just how much more growth does Pinterest have in it? Pinterest has mainstream appeal to be sure, and it will grow, but it’s arguably not the next Facebook or Twitter. How many more hardcore users are out there for it to acquire?
  • Can Pinterest maintain its focus? One of Pinterest’s most beneficial attributes is the character it has. With registration open to everyone, it will be interesting to see if it can maintain that character.
  • What will happen to quality? If newcomers flood Pinterest, will the quality of the network and content shared on it be compromised? Of particular concern: spammers.
  • Will Pinterest scale gracefully? Scaling a popular social network isn’t always easy. Although the rapid evolution of technology has given startups the tools they need to avoid becoming the next Friendster, scaling without a hitch isn’t guaranteed. Just ask Twitter.

The answers to these questions could have a significant impact on brands investing in Pinterest. After all, if Pinterest fundamentally changes, quality goes down, or scaling issues start to become an issue, brands may find it more difficult to capitalize on the opportunity.

On the other hand, if the next phase of Pinterest’s evolution proves to be as impressive as its first, look out: brands that got in early and are doing things right could be the first to find that social media ROI everyone is looking for.