Why your inbox is being flooded by LinkedIn by Jessi Hempel @FortuneMagazine May 10, 2013, 6:39 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons FORTUNE — What’s up with LinkedIn? Suddenly it’s everywhere. Last week, as I finished up teaching a dozen masters students in publishing, I told them to keep in touch. Nobody called. No one emailed. Seven of them requested to connect with me on LinkedIn. What’s more, lately my inbox has been teeming with social notifications beyond the simple “please join my network” request. Friends and colleagues are “endorsing” me for skills I haven’t even thought up or “congratulating” me when I add a new job (“adjunct professor”) to my profile. And then there’s LinkedIn Today, a social newsreader that provides some a better-cultivated deep-read of the pertinent news in my industry than the soon-to-be-defunct Google Reader GOOG I once curated myself. I’m not imagining things; the numbers prove it: In the past year, LinkedIn LNKD has seen a 24% grown in number of monthly visitors in the United States to 46.3 million — and that’s not counting the increasing number of folks who use the service on mobile devices. Even more interesting, the service has seen a 52% spike in time spent on the site — in March, users spent an average 1,072 minutes on LinkedIn.com. MORE: General Motors’ $6 billion truck All of this has happened while the unemployment rates have dropped over the past year. A decade ago when LinkedIn got its start, the social network was largely understood to be a database for crowdsourced digital resumes; for years, it survived because people turned to it when they were looking for jobs. These days, however, it’s easier to buy the marketing promise that LinkedIn is more than a job board; it has become a useful tool for managing professional life. While many of LinkedIn’s users have experienced that change seemingly overnight this spring, in truth it’s the product of a rigorous approach to development on the part of LinkedIn’s executives. Shortly after the company’s 2011 initial public offering, LinkedIn’s engineering team embarked upon “Project Inversion,” a two-month process in which product development largely stopped and the company rebuilt its infrastructure from the bottom up. In a February 7 earning call, CEO Jeff Weiner explained, “Our success enabled us to materially accelerate the speed with which we released new products from once every two weeks for the entire site to as much as twice per day for each individual product.” The result: During the last four months of 2012, LinkedIn introduced more new products than any other quarter in the company’s history — and things continue to accelerate. Notable products include a new version of the LinkedIn profile that is called the “professional profile of record” and a new version of the “people you may know” tool. Perhaps in result, LinkedIn said it saw invitations increase 80% from 2011-2012; that translates into a lot more “join my network” invitations in your box. MORE: So who’s making money publishing on the web? Then there’s the new “endorsement” tool that, much like a game, lets you endorse people in your network as possessing skills that LinkedIn suggests. (So far, 28 people in my network have endorsed me for journalism; more perplexing, eight have endorsed me for press releases. I’ve never written a press release.) At the end of its fourth quarter, LinkedIn reported that its members had generated nearly a billion endorsements in the four months since the tool went live. All of this activity is useful — to LinkedIn and to use — because it turns unstructured data (what I know I’m good at) into structured data (what you know I’m good at). And as more of our colleagues join it and use it, it becomes a more useful tool for communications. Like, say, reliably keeping in touch with my former students.