Sony has corrected its previous statements about the Vita's ability to support multiple PSN accounts, again. Contradicting what we'd been told before, a PSN account is not merely tied to a memory card, Sony told Wired. It's tied to both the card and the system.
That means that switching accounts is not as simple as it sounded. "If a second person is using your Vita," a Sony rep told Wired, "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."
You're extremely unlikely to be willing to completely flash your Vita every time you want to switch accounts, so you can go ahead and forget about keeping separate US and Japanese PSN accounts, for example. And the Vita just became slightly less useful.