The X and O confirm/cancel difference so many Vita/PSP games pushed me to get a FEB and sell off my import Vita. It has been a bigger pain in the ass than I anticipated, especially going back between the PS3 and the Vita.
The units are largely the same, but I did notice that my US Vita seems to be a little heavier. Not sure if it's the 3G antenna or whatever, but I noticed it immediately. I like the change, makes the unit feel a bit more solid. I also noticed a pretty big difference in the settings. In my import Vita, there wasn't "Auto-Start" settings like there is on the US Vita. Appears this controls apps that start when the Vita starts, which is pretty cool.
Anyways, I picked up 280 selling my JP Vita and 8GB card, and I had some store credit to secure the balance.
Also, the grips with triggers is a great buy. Playing FIFA and Uncharted with them is a better experience. Playing touch screen only games like Escape Plan feel better without the grips though. Luckily they pop on and off easily.