Usability: A Requirement for Security
This article has a number of good points to consider when designing "secure" systems.

"For security to be effective, it has to be convenient. That means designing to relieve the burdens of everyday users and system administrators instead of adding new ones. Companies that ignore this will fail to increase security."

"Strong security is more than just technology. The lack of usability of today's technology means that only the most sensitive data handled by the most paranoid employees stands a chance of being protected properly."