Lion comes with this nifty option called AirDrop, which allows users to share files directly. In many environments, this represents a perceived security risk (whether real or not) and must be disabled. To disable AirDrop:
defaults write com.apple.NetworkBrowser DisableAirDrop -boolean YES
To turn it back on:
defaults write com.apple.NetworkBrowser DisableAirDrop -boolean NO
This is done per-user and so can also be done via Managed Preferences, profiles and/or at imaging time.
