I am very happy with this. I get very very VERY annoyed with deactivating and re-activating my PSP for using stuff from my Japanese and U.S. PSN account. Source http://www.wired.com/gamelife/2011/12/vita-accounts/
Pretty much this. If I ever decide to get one of these then I won't ever need to do it, considering I only use one PSN Account that I use frequently anyway. But it is useful for anyone who could or would want to use it.
I guess it's the little things that will make it more successful. I may use the feature, if my girlfriend doesn't get her own, so I guess it's good news.