What’s been happening this week?

Well, just in case you needed some confirmation as to why you’ve gotten your business involved in social media marketing in the first place, new data reveals the number one reason. Think you know what it is?

It also looks like Facebook’s U.S. growth may finally be slowing down, but Twitter is on the rise. While that’s happening, new kid on the block, Pinterest, is growing and boosting sales for small business.

And we find out why email best practices are linked to a strong ROI and how Facebook borrows another idea from Twitter.

Take a look at this week’s hot topics.

1. Facebook’s U.S. Growth Slowing, But Twitter’s on a Tear [STUDY]

A new study by eMarketer estimates that Facebook’s growth in the U.S. will drop to the single digits this year for the first time, while Twitter’s growth will expand by about 20%.

Bottom Line: At the end of 2011, Facebook claimed about 133 million U.S. users, and according to one analyst, its global audience is expected to be 1 billion this August. Twitter recently hit the 200 million mark. These figures still support Facebook and Twitter as the big social networking sites and should be part of your social media marketing strategy.

2. Pinterest’s Rapid Rise Boosts Small Business Sales

The visually fueled site has received more than 103 million total visits in February alone. One fine art photographer credits Pinterest for amplifying his online sales to 50% of his current business. And Greek yogurt maker Chobani has seen huge amounts of referral traffic.

Bottom Line: Pinterest is worth exploring for online retailers, especially those with products that have a strong visual element. As with any social network the key is participating with the community to gain the most traction.

3. The Number One Reason SMBs Go Social Is…

(Cue drum roll.) According to new data, the number one reason (49 percent) small businesses get involved with social media is to find new customers. You already knew that though didn’t you?

Bottom Line: If you’re going to be successful using social media to find new customers you’ll need to be actively engaging on the networks where your current customers are. They’ll help you find new customers. Make sure it’s easy for people to find you and for people to share your content with their friends. These online endorsements are the key to reaching new customers. Be sure to keep reading the blog for social media marketing tips.

4. Email Census shows link between email best practice and strong ROI

In a recent census of the email marketing industry, companies consider ROI from email marketing to be higher than most other digital channels including social media marketing. Moreover, the study found that companies adopting best practices and using their email service provider’s functions beyond basic “batch” and “blast” are significantly more likely to see a strong financial return from their email campaigns.

Bottom Line: As we’ve been saying all along email marketing should be the backbone of your online marketing efforts. All other digital channels should work as an extension to email with a focus on eventually moving those connections to your email list.

5. Facebook Launches “Interest Lists”

Facebook has added new functionality that allows users to create lists based on interests, very similar to lists on Twitter. Users can add Pages and profiles with the subscribe button enabled to their lists to see a clean newsfeed of updates based on their interests. User generated lists can be public or private. Public lists will be available for user’s friends to subscribe to as well.

Bottom Line: It’s too soon to tell if lists on Facebook will take off but it makes sense to encourage your Facebook fans to add your Page to their lists (which they can do from the gear icon on the new Timeline layout for Pages.) Furthermore, it could be good for high profile members of your company to create curated lists that include your business for users to follow. Interest lists may prove a good way to bypass Facebook’s EdgeRank Algorithm, that is, if users find your content interesting enough to want to follow it more closely.

What stories have you been buzzing about this week? Share them in the comments.