More or less what Leo Ames said, you'd need another memory card and everytime you switched regions you actually have to reset your vita in the settings. YMMV but it's more or less a hassle.
I wish Sony would just treat each region equally in terms of deals and available games so that people didn't have to jump through hoops to access content from other regions. Since the ps3 is capable of multiple regions I'm not sure why they restrict this feature on their handhelds.....