Tomio Geron

For fast-growing technology start-ups, there are many approaches to employee hiring and retention.

Two of the more successful Internet start-ups, Facebook Inc. and Zappos Inc., have very different methods, each with different goals: Facebook wants to hire entrepreneurs even if that means they will eventually leave, while Zappos wants to hire the best people to fit its culture and figure out how to keep them.

It all started with a “stupid” idea and a message about pinot noir.

Two of the founders of Twitter Inc., Evan Williams and Biz Stone, talked about how the micro-blogging service began, the challenges it faced and an eventual potential IPO, at Startup School, an event organized by Y Combinator held at the University of California-Berkeley on Saturday.

While many venture firms have dialed back their investments amid a punishing economy, Sequoia Capital has made about 20 seed or Series A investments in the past 12 months, more than in the prior two years.