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enlightening point of view from Microsoft.

http://www.microsoft.com/technet/network/wifi/hiddennet.mspx

"Therefore, using non-broadcast networks compromises the privacy of the wireless network configuration of a Windows XP or Windows Server 2003-based wireless client because it is periodically disclosing its set of preferred non-broadcast wireless networks. When non-broadcast networks are used to hide a vulnerable wireless network?¡é?€?¡±such as one that uses open authentication and Wired Equivalent Privacy?¡é?€?¡±a Windows XP or Windows Server 2003-based wireless client can inadvertently aid malicious users, who can detect the wireless network SSID from the wireless client that is attempting to connect. Software that can be downloaded for free from the Internet leverages these information disclosures and targets non-broadcast networks."
Rod
http://www.networksetup.com