Let’s say you have Monster Hunter Portable 3rd and a friend has the same game installed on PlayStation Vita. Can you play together? The answer is yes. PlayStation Vita can play downloadable PSP games and communicate with PSP for ad-hoc play.
While it isn’t as prevalent in the West, ad-hoc games are quite popular in Japan especially with respect to the multiplayer hunting genre. And if you like the Vita’s OLED screen you can play a digital copy of God Eater Burst on it and be the envy of your Aragami hunting group. Also a plus for Lord of Apocalypse, which Square Enix announced for PSP and PlayStation Vita.