Today Sony's associate brand marketing manager Crystal MacKenzie has confirmed that PS Vita PSN accounts are linked to the handheld's memory cards and not the device itself for those wondering.
Essentially this means those who like bringing their gamer profile and downloadable games over to a friends house to show them off will probably like the PlayStation Vita since the PSN accounts are bonded to the memory card they're downloaded to.
To quote from GameInformer.com (linked above): "Your PSN ID is bonded to your memory card and your memory card is bonded to your Vita," Sony associate brand marketing manager Crystal MacKenzie told Wired.
"So if you wanted to change different PSN users but use the same memory card, you would need to go factory reset."
So accessing your PSN account and games is as easy as swapping out the memory card they're installed on. Sounds simple enough. If you have too much media for one of Sony's spendy storage devices, you can have your PSN account linked to multiple memory cards.