Conrad told you earlier that a few Vita games were up on the PlayStation Store tonight, but now the full Vita PS Store has launched. This is the day that importers with Japanese Vita systems and US PSN accounts have been waiting for.
There's not much content on the Vita store yet, but there are a few games to buy as well as demos and videos. If you have PSP games or PS Mini titles, some of them are available for download to your Vita now. The PSOne titles are not downloadable yet.
I'm a bit concerned that some PSP titles aren't downloadable, with the message "cannot download using a PS Vita system" replacing the download button. Here's an example of some of my own PSP games that aren't downloadable right now:
Plenty of other PSP games are downloadable, though. I've got God of War: Chains of Olympus pulling down now. It's not quite launch yet, so Sony could still be working out some bugs with the PSP offerings.
If you've got a Vita, check out the PS Store on your system now!