Hold it right there, person about to update his or her PS Vita's firmware to the latest version, which is v1.80! Ask yourself the following questions:
1. Do you have another PSN account located in a different region (say, Japan, Europe or North America), that you intend to use for downloading content or games?
2. Do you have more than one Vita memory card?
If you answered "yes" to the first question and "no" to the second, you should hold that update and go get yourself an extra memory card right now, because in addition to PSone game support and other nifty features, the Vita's new v1.80 firmware also locks your memory card to your Vita's current PSN account! If you don't have a PS3 backup or extra memory card, you lose access to any data not tied to the current PSN account, including saves and DLC.
Sony has pulled a bit of a dick move and partially closed the "system restore" loophole that allowed players to buy cross-region downloads by backing up their data (to PCs, PS3s or extra memory cards), then wiping their Vitas and restoring them to an appropriate region.
It's not as bad as it looks, though. Physical copies of import games are still region-free, and can be played regardless of the buyer's PSN location (with some MMO-type exceptions). Most folks affected will be importers who use only one memory card between all their accounts, which should be the minority case among dedicated import players.
That said, it's a sad day when any company tries to pull region shenanigans, and importing just became a more tempting prospect thanks to North Americans getting the shaft over the Vita's PSone game selection. For shame, Sony!