A rogue access point on a company that takes its wireless LAN security seriously still painful to detect: You can see how even with a strong set of policies, it's easy for an employee to subvert them. You might understand now why some companies have strict bag searches for employees entering and leaving the building.
Those of you who saw the Al Pacino movie The Recruit will remember that one of the most plausible technology plot points involved a hidden USB hard drive. (Of course, CIA computers probably have their USB drives sealed and USB drivers set to restrict access, but you never know.)
One of the factors that makes rogue wireless access points difficult to cope with is that local wired networks are often security free. This is changing, of course, with the rise of VLANs and secure fileserver mounting. The Recruit 2: Revenge of the Nerds will obviously feature someone with a micro-Wi-Fi-antenna.