Yes, day one.
I really enjoyed the PSP, and now I want more horsepower, touchscreen, motion sensor and second analog. And I'm really hyped with some Vita games that aren't going to be in my Android/iOS gadgets.
I have a high end Android phone and a high end iPod, and love some of their games, but I miss AAA hardcore games and some popular IPs there, and proper controls (physical pad, 2 analogs and buttons) for certain genres that I love.
Even if smartphones had all this stuff, their market is saturated with free/$1 games so that means that high budget games don't fit here, so I think I'll need a handheld console like Vita these years.
In addition to this, Vita will have a shit ton of PSP, PS1, Minis and Neogeo games since day one.
And it will have a decent price for it, so I'm in.