Excerpt from Rework by Jason Fried & David Heinemeier Hansson (creator of Basecamp)
Instant cultures are artificial cultures. They're big bangs made of mission statements, declarations, and rules. They are obvious, ugly, and plastic. Artificial culture is paint. Real culture is patina.
You don't create a culture. It happens. This is why companies don't have a culture. Culture is the by-product of consistent behavior. If you encourage people to share, then sharing will be built into your culture.
Culture is action, not words....
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So don't worry too much about it. Don't force it. You can't install a culture. Like a fine scotch, you've got t to give it time to develop.