I bought it for my nephew but I think I will hold on to it for few more weeks. I got it from Play (an Uncharted and 8GB card bundle) and it is a very good piece of kit. I bought the original PSP on the day it came out and this is as exciting.
The screen is brilliant, I watched a trailer of Men in Black 3 and I must admit the screen is better than my ASUS Tranformer's screen. It is sharp and the colours just pop out of the screen. I have already completed The Uncharted and the gameplay is really good.
I was a bit apprehensive as I saw many reviews referring to its size as being to bulky but, honestly, it is smaller than I excpected. Yes, it is a little bit bigger than the PSP and you probably wouldn't put it in your pockoet. This is not, however an issue and once the price comes down a little bit I will get one form myself too (I would have done so already if it wouldn't be for the fact that I drive to work and not commute on the train).
All in all if you had the original PSP you should definitely get PS Vita. The only thing that Sony is missing here is the price of the games, espacially digitial downloads. 40 pounds for a FIFA? Despite it being a very good game (I play a demo) no game for a handheld is worth 40 pounds (well maybe Assassins Creed when it comes out).
If the prices will go down, including the hardware, this will sell incredibly well.