Somewhere, deep in the heart of Sony's underground facility/HQ, an executive is punching an intern. Partly this is because he can; mainly, it's due to the recent confusion over the Vita, PSN accounts, and the frustration that stems therefrom. Initially, the company had indicated that the handheld would have a limit of one PSN account per system; users would only be able to use a different one by reverting the Vita to factory settings, thereby erasing all user data. After this, in an exchange with Wired, associate brand marketing manager Crystal MacKenzie stated that the reports we false. Rather, "Your PSN ID is bonded to your memory card and your memory card is bonded to your Vita [...] So if you wanted to change different PSN users but use the same memory card, you would need to go factory reset." In short, user information would be tied to the memory card only: Vita owners would be able to use multiple PSN accounts on the same system, though this would require using a different memory card for each account.
As it turns out, this may not be the case. Wired released a follow-up story after receiving word from a Sony rep that "PlayStation Vita is intended to be played by only one user." He went on to say that the owner's PSN account is in fact linked to the hardware, "which means that if a second person is using your Vita, it's not just a case of switching out memory cards, it's clearing out all of your saved data on the Vita itself when you do the factory reset."
While it may seem like a rather trivial thing, one of the advantage of multiple accounts is that gamers can pick up titles from different regions. So if you were looking forward to enjoying some non-North American downloads - this is, of course, assuming you're living in either Canada or "Mmmerica!!" (yes,that is the proper spelling of my country's name) - looks like you're out of luck, unless Sony decides to remedy this in a firmware update.
Time to go punch an intern.