Remember how you could change the PSN account on your Vita without changing your memory card and without formatting it? Well, as of firmware update 1.80 the fun is over. Your memory card is now locked to one account and this can only be changed by formatting the memory card.
If you switch accounts you are now greeted by this wonderful message:
Sorry for the bad picture (screenshot function doesn't work at that point), the whole message reads:
If you select "Cancel" the Vita will behave as if no memory card was inserted.
The memory card inserted in your system is linked with the following Sony Entertainment Network account.
To use the memory card with your PS Vita system you must format the memory card.
If you format the memory card, all data on the memory card will be deleted.
I guess this screws up more people than just me. It's an especially wonderful gift considering they just gave us PSOne games which a lot of people (or at least some) have probably spread across multiple accounts.