Listening to this 8 minute interview with Dave Girouard of Google, I learned that, to maintain the entrepreneurial spirit, the following four things are, for example, done:
1. People, who work for the company, are given as much freedom as possible.
2. The organizational structure is kept very flat.
3. Constant experimentation is done with compensation systems.
4. Research & Development is spread out across the world. Ideas come from everywhere.