eric kanitz,
I'm sorry this is causing you so much frustration. Unfortunately, I don't think I bare good news: The issue with the import and export methods is that they're locked down in Acrobat/Reader for security reasons. Acrobat/Reader cannot allow an arbitrary PDF form to access a user's system without their knowledge and explicit permission (hence why using the import method with a filename does nothing and you're required to use it without any parameters in order to prompt the user).
This is documented on all the "import*" and "export*" methods of the Doc object in the
JavaScript for Acrobat API Reference (I believe the xfa.host.importData method executes in the same security context).
According to page 32 of the same document, these methods may take a file path parameter only when executing in a privileged context which would imply, for example, that the call to import/export is executed within a trusted application function.
In conclusion, I don't believe you can import/export data on a user's hard drive without user intervention from a simple PDF form. If you could support a connected scenario, then you could use a web service to retrieve and post the form data but then the user would still have to be prompted by Acrobat/Reader in order to allow the form to communicate with the web service URL (again, for similar security reasons).
As for your questions, should you implement something to execute these methods in a privileged context, it should work in Designer's Preview Mode.
Stefan
Adobe Systems
More answers at
Stefan Cameron on Forms.