You may recall that earlier Sony said there will be one PSN account per Vita. This naturally made many users mad or just generally disappointed. As a frequent importer this could be extremely annoying.
Apparently the account information is tied to the memory card and not the actual device. However the memory card is tied with the Vita itself. This means you can have a memory card for each account you want to use, but it will only work on your vita. You can also change the account tied to the memory card, though you must format it first.
This is definitely a plus, but a costly one. Sadly there no mention of how this would affect the trophy system, so ideally this will let you use the content on one universal account. Hopefully more details will come out as we get closer to release.