Security company @stake has posted an advisory that Palm OS handheld computers can be accessed by someone if they have the proper developer tools. This means that if you lock your Visor with the Security application and then lose your Visor, someone could still access your data.
According to @stake, the developers kit that debugs Palm OS devices can be activated even if the handheld is locked. This would allow someone to get the security password, thus getting access to the device.
I've always kept important information in an encrypted application like STRIP, particularly after reading about Network HotSync issues. Search our software discussion area for Security alternatives.