This is a good piece by Adam Lashinsky outlining the culture of secrecy at Apple.

Apple created an elaborate and unnerving system to enforce internal secrecy. It revolves around the concept of disclosure. To discuss a topic at a meeting, one must be sure everyone in the room is “disclosed” on the topic, meaning they have been made privy to certain secrets. “You can’t talk about any secret until you’re sure everyone is disclosed on it,” said an ex‑employee. As a result, Apple employees and their projects are pieces of a puzzle. The snapshot of the completed puzzle is known only at the highest reaches of the organization. It calls to mind the cells a resistance organization plants behind enemy lines, whose members aren’t given information that could incriminate a comrade. Jon Rubinstein, formerly Apple’s senior hardware executive, once deployed the comparison in a less flattering but equally effective manner. “We have cells, like a terrorist organization,” he told Business Week in 2000. “Everything is on a need‑to‑know basis.”

Perhaps a strong generalization of how Apple differs from other Silicon Valley companies:

Apple’s culture is the polar opposite of Google’s, where fliers announcing extracurricular activities — from ski outings to a high-profile author series — hang everywhere. At Apple, the iTunes team sponsors the occasional band, and there is a company gym (which isn’t free), but by and large Apple people come to work to work. “At meetings, there is no discussion about the lake house where you just spent the weekend,” recalled a senior engineer. “You get right down to business.” The contrast with the non-Apple world is stark. “When you interact with people at other companies, there’s just a relative lack of intensity,” said this engineer. “At Apple, people are so committed that they go home at night and don’t leave Apple behind them. What they do at Apple is their true religion.”

Perhaps one day when I visit the Apple campus I will indulge in getting the shirt that has the following printed on the front: “I VISITED THE APPLE CAMPUS. BUT THAT’S ALL I’M ALLOWED TO SAY.”