The traffic-driving impact of The Big 3 social networks – today, let’s rank them as Facebook, Twitter and Pinterest – is being constantly measured, calibrated, then re-measured and re-calibrated, it seems. This is important as marketers want to know on which networks it would be wisest to maintain a vibrant presence. The answer: all three. But it’s clear that one of these Big 3 is not just driving traffic, but big-ticket sales. Hint: it ends with “interest.”

As we write, the world is playing countdown to the biggest tech IPO in a decade. In a matter of hours, we’ll know how many billions (north of $100 billion) will add up to the value of Facebook. As we ponder all those zeros, here’s an interesting infographic on the 901 million-pound gorilla’s globe-spanning growth.

For some time now we’ve been delivering to SMI readers a “Social Media by the Numbers” roundup, a summary of the big numbers and the big picture that are driving social. Our newsletter subscribers know this well as they get it in their in-box at the start of every week. Here, we’ve put together a longer version that look back over the past few weeks so those of you are not familiar with it can get a glimpse. Enjoy!

There are now more than 46 million avid “gadget” gamers in Western Europe, and Britain leads the league table by a surprising margin. Looked at another way, over 40% of Europe’s smartphone users are using their sleek new handsets for gaming, a phenomenon triggered by the success of Angry Birds, Farmerama and Draw Something. Gaming has now leap-frogged music as one of the most popular uses for smartphones.

As data geeks here at SMI, we’re into the big numbers and the big picture. That’s why we send out each week to our subscribers a super concise bulletin of the big data points that are driving the sector. We informally call it “Social Media: By the Numbers.” With these data points, we tell you the big research insights, innovations and strategy points that explain what’s working and what’s not working. Today, I’m introducing a longer version that I will will occasionally reprise.

Last week we got the latest IAB figures showing a booming digital ad sector, helped by the continued rise of social + mobile + video. Today, a new global digital ad report is out, showing social search is one of the fastest growing segments of online search, which itself is still far and away the largest revenue-generator in digital advertising.

If we sound a bit too cheery here at SMI lately, I can assure you our optimism around the social sector is well-founded. The trifecta of social, mobile and video are transforming not just the world of marketing, but business as well. This powerful trio is driving sales, helping brands hone their marketing and improving customer relations, building deeper bonds that could lead to improved messaging and improved products.

The IAB UK’s latest tally is just out this morning and again the figures make for bullish reading material. Once again, the digital ad growth in the UK is experiencing crisis-defying growth, and the fastest growing part of that is social media marketing. Let’s dig into the numbers.

We came across an interesting infographic that details one of the burning questions on the lips of all digital marketers: who exactly are these Pinterest phans? What do they do? What do they earn? And how is that they have made this network the fastest-growing out of the gate?

Predictions of the imminent decline of blogging has been with us for some time. Even we wondered about its longterm future as recently as a year ago, pointing to figures that showed, despite the success of Tumblr and Posterous, growth rates were leveling off. A new tally by blog trackers at Nielsen though warns us not to write the obituary just yet, even as blogging faces a new threat. Hint: it begins with a “P.”