Adam Smith, co-founder of San Francisco-based Xobni, is hanging up his hat and leaving the company. He’s giving up his position as the chief technology officer to Peter Monaco, formerly of TellMe. Smith didn’t say what his plans were. The company has raised $30 million in VC funds from Khosla Ventures and others such as RRE Ventures, First Round Capital and Cisco.

I met Adam about four years ago. He and co-founder Matt Brezina had just started their company and we quickly found that we shared a lot in common — mostly around the notion of using the email inbox as a social networking utility. Over the years, I got to spend a lot time with the young co-founders and about two years ago, I was asked by MIT Technology Review to write a profile of Smith for their 2008 “Under 35 Young Innovator” series. During the reporting process, I got to know the then 23-year-old Smith really well. I also learned about his early attempts at entrepreneurship, his (mis)adventures at MIT and of course, how he met Brezina.

None of that made it into the final story and neither did the rest of the fun stuff. I also learned that at age 13, he already had plans to work for Microsoft and eventually start his own company. Not willing to wait, he started a shareware company called Viratech when he was 13. The two products from that company — Time Manager and EBMailer — both cost $20 each and sold really well for 10 years. Smith, who graduated from MIT with a computer science degree with emphasis on machine learning and large-scale systems, has become one of my favorite entrepreneurs.

I know whatever he does next will be amazing. And to think he’s only 25!