It's bad for those hoping for cheaper memory card prices though. I would assume there's layers of encryption involved when a card is bound to a system, which will be next to impossible for third-parties to replicate unless the Vita is hacked.
Depending how it works, it may be impossible to reuse a card on another system as well -- which would cut out secondhand sales of cards altogether (may be what Sony is aiming for here).
I read a quote somewhere from a Sony rep saying that you can remove the link to a PSN account by formatting the memory stick back to factory defaults. Which, like NeilR said, is way better than the previous report of only being allowed to tie a single PSN account to a Vita system.