PS Vita - Multiple PSN accounts on One Memory Card
It is possible!
After doing some experiments I have found out some interesting things about the Vita. Everyone currently believes that you need two memory cards for two PSN accounts. This is not so.
You can back up your memory card and the Vitas internal storage to each PSN account on your PS3. So for example you can back up your UK account to your UK PSN account and your Japanese account to your Japanese PSN account on the same PS3.
When you have done this you then need to format the card or when you sign in with your other PSN account on Vita it will tell you the PSN account the memory card is tied to is a different one and that you need to format it.
Now connect your Vita to your PS3 signed into the account you want to use, restore the data and bingo your done. Do the same to swap back to your other account BUT don't forget to back up again first if you have any play progress or downloaded demos etc.
The Vita will back up ALL the content on your memory card to your PS3 including demos and music etc.
By Kristian Salkeld