Was waiting for this to happen (and fully expected it to). Kept checking every hour or so online since Friday.
My fallback plan was to buy the 2 of them at Best Buy at midnight Monday/Tuesday morning.
Now that Amazon is doing it (the same as everyone else), I am getting MLB 12 for the PS3 and the Vita for around $58 ($60 for PS3, $20 for Vita after combo purchase and after $20 coupon code for buying my Vita through Amazon) - essentially getting the Vita version for free and paying less for both of them than I would just for the PS3 version at retail.
I am SUPER looking forward to playing this game on the Vita. MLB 10 for the PSP is by far my most played game on any system (not including Civ 4 on the pc). I'll be pretty much playing Franchise mode on the Vita almost entirely (whilst I watch baseball games on the tv!) and playing online on the PS3 version.
Here's to hoping Diamond Dynasty mode is as amazing as it sounds and that next year they allow you to play exhibition dynasty games against your friends online.
P.S. - this game is coming out at the PERFECT time. I've got a roughly 6 hour car ride on Friday morning and then back home on Sunday morning where I am going to be playing the ish out of this game.
Double P.S. - I am LOVING my Vita so far. Between MLB 12, Uncharted, and Tales From Space: Mutant Blobs Attack (which, honestly, is the most fun I've had playing a video game in quite some time), I am getting my money's worth for the year easily.