Several years wiser, Mr. Hoffman — as the executive chairman — focused on his strengths: product and high-level strategy. It also gave him time to accept a job at Greylock.

Today, Mr. Hoffman splits his time between Greylock’s offices on Sand Hill Road in Menlo Park, Calif., and LinkedIn’s headquarters here in Mountain View. Again, he senses that a new Web is stirring. In the same way that social media redefined the Internet, he sees another tectonic shift on the horizon.

This one, he believes, will be driven by data. Mr. Hoffman has been investing in companies that are data-driven or starting to work with data in interesting ways. For instance, even though two Greylock investments, Shopkick and Groupon, focus on retailing, both aggregate a huge volume of information on user spending habits. LinkedIn, too, has been trying to leverage the data on its site by, for example, making it more searchable.

IN Silicon Valley, it’s often said that the founder is the start-up. Friends of Mr. Hoffman describe him as a walking version of LinkedIn — data-intensive, straightforward, useful. In some ways, Mr. Hoffman and his company face similar challenges.

LinkedIn, which has soared in value, is under increasing pressure to perform. Though its membership has roughly doubled annually for each of the last seven years, many wonder if the company can possibly sustain its momentum. LinkedIn can’t afford a bad quarter: one miss could hobble the company, analysts say, by slamming its share price and encouraging its best engineers to jump to the Next Hot Thing.

“The problem is, most people are not like Reid,” said Joichi Ito, the director of M.I.T. Media Lab, who has known Mr. Hoffman for many years. “Most people waste their time, so the question is, can a work-oriented site become extremely popular, when many people are not as invested in productivity?” Mr. Hoffman himself is feeling the squeeze. But he tries not to pay attention to the markets and says he has checked LinkedIn’s stock price only six times since May.

“The thing I’m working on with LinkedIn in is to create something massive and effective; the strategy horizon is three to five years,” he said.