Of course you know about the "pinboard" site Pinterest, which attracts 20 million visitors a month and has been valued at, oh, a cozy $1.5 billion. And Spotify, the Internet music service, is a whisker from being a household name, with more than three million paying users and a reported $220 million funding round waiting in the wings. To have created either company would be a pretty amazing lifetime achievement.

The fact is, though, the two companies' founders are just getting started.  Pinterest's leaders--Ben Silbermann and Evan Sharp--are each just 29 years old. The serial entrepreneur behind Spotify, a Swede named Daniel Ek, is also a year shy of 30.  In the age of Mark Zuckerberg, it's easy to shrug at tales of fabulous success among the improbably young. But seriously, now: How many great, disruptive businesses had you launched by age 29?

Odds are, quite a bit fewer than have been created by Ek, Silberman, Sharp or any of the 30 incredibly accomplished 20-something entrepreneurs identified in this year's 30 Under 30 ranking. Not to brag or anything, but Inc. has a pretty respectable record at indentifying future superstars before they're known in this ranking. Prior honorees have included Mark Zuckerberg (Class of '06), Aaron Patzer (2008), and Lauren Bush (2010), to name just a few.

You probably won't have to wait long for the class of 2012 to yield its own crop of mega-overachievers. One of them might be Jeremy Johnson, the 28-year-old college dropout behind 2tor, an online educator that is partnering with Georgetown, UNC-Chapel Hill, and USC to deliver college- and professional courses that are every bit the equal of those insitutions' classroom offerings.  Ben Milne, a 29-year-old serial entrepreneur, is undercutting fee-heavy credit card companies with Dwolla, his cashless payment start-up. And Lucas Buick and Ryan Dorshorst, the 29-year-old co-founders of Hipstamatic retro photo filters for smartphones, inked a deal earlier this year with Instagram, the photo sharing app that Facebook bought for $1 billion in April.  (Instagram, in turn, is led by 30 Under 30 alums Kevin Systrom and Mike Krieger, class of 2011.)

Some observations about this year's 30 Under 30 honorees:

  • They're solving big problems.
    These young entrepreneurs are going after sectors that are in desperate need of reform, such as health care and education. Zach Sims and Ryan Bubinski, co-founders of Codeacademy, and Adam Pritzker, Matthew Brimer, and Brad Hargreaves, the team behind General Assembly, are teaching the business and technology skills that are critically important in today's job market. Nathan Sigworth's Pharmasecure is working to combat counterfeit drugs in developing countries, while Aza Raskin's Massive Health app, the Eatery, creates a community that encourages healthy eating. GiveForward founder Desiree Vargas Wrigley is helping families raise money to cover the costs of medical emergencies.
  • They're creating jobs--lots of them.
    While unemployment stats are consistently bleak and the jobless rate among young people a staggering 23%, the Inc. 30 Under 30 are creating jobs--and at a higher rate than ever before. This year, the Inc. 30 Under 30 employs more than 1,800 people, up 73% since last year. The median number of employees at companies on the list is 25, up 92% from last year. The biggest such job creators are serial entrepreneurs like Steve Espinosa (Appstack, a mobile website creator), and those who are well beyond start-up stage and have been in business for more than five years like Ilya Pozin (Ciplex, a web designer).
  • Manufacturing is back.  
    Inc. has already noted that American manufacturing is making a comeback. The young manufacturers who rank among the Inc. 30 Under 30 this year care about where they do business, too. Take Rachel Weeks, founder of School House, which makes fashion-forward college clothing; she brought her manufacturing from Sri Lanka back to Durham, North Carolina and, in the process, found a new and meaningful brand identity. Ziver Birg of Zivelo makes kiosks in Marion, Indiana and helps keep 200 metal fabricators employed at a local factory.
  • They're still young, but older than before
    This year, 70% of the Inc. 30 Under 30 founders are older than 27. And not one was younger than 25. It makes sense, if you think about it. GenY, a highly entrepreneurial generation, is growing up. Will the group that follows be as smitten with creating new businesses, and as comfortable taking on the risk? We hope so.
  • The future's in mobile
    We could cull together an Inc. 30 Under 30 made up entirely of mobile app makers, but we narrowed the field of applicants to those with truly innovative products. Among them: Geoloqi, which provides location-tracking of people in potentially life-threatening situations for a U.S. Department of Defense contractor; and Heyzap, which has created one of the largest mobile gaming communities in the world.

Check out the full Inc. 30 Under 30 list for yourself; read individual entrepreneur profiles, and watch them in videos. And be sure to cast your vote for your favorite.