I have used at least 100 personas over the past decade.
But I've gone out of my way to avoid associating any of them with my meatspace identity. I compartmentalize by VM, Internet connection path via VPNs and Tor, contacts, activities, interests, and language.
> Should the visitor be forced to list these sensitive identifies in order to enter America?
I wouldn't. Because I'm confident enough that they couldn't be associated with me. Not without concerted effort by the FBA and/or NSA. Also, I have retained no records of all but ~10 of them, so I couldn't disclose them if I wanted to.
So bottom line, if you have sensitive identifies that you wish to keep private, they had better be thoroughly compartmentalized. Nobody who knows you in meatspace should know anything about any of them.