I recently used a PS Vita at two different gamestops in my area and played a little through the uncharted demo, and wanted to give my opinions.
First, let's talk about the main menu. It looks nice, works nice, but there are dots on the screen on the left to show pages you have to put apps. The issue is even with empty pages the dots are still there, but you can't turn to that page, if it makes sense. Not a big problem just annoying. None of the menu is controlled optionally by buttons, it is ALL touch.
I took a minute or two to just look at the device and press all the buttons. The device is rather light, it's VERY large, the screen had a few finger prints on it (never a good sign), but the buttons were nice, the d-pad and x, square, triangle and circle buttons were much smaller than the PSP's, and were closer together. I figured this might be an issue but it actually made navigating much easier and made the buttons much less awkward. The L and R buttons were a little awkward to use, kind of hard to describe, but just a little awkward, at least because I have decently big hands. The analog sticks had almost no resistance, which I was very disappointed in. Unlike the PS3 controller's analog sticks, putting the slightest pressure forward or in any other direction on the analog sticks results in it slipping around. They are very small as well. They were decent considering they were on a handheld. It has a strange...slight cone type thing, which doesn't seem to do much, it may help prevent grinding down on the sticks, because the ps3 would often "sand" off the analog stick. The buttons and D-pad are very clicky.
On to the Uncharted Demo. This is where I saw the really dumb sides of the Vita. First, I start out the game. It takes a bit to load, none of the intro videos are skip-able. So you get to the main menu, and my first instinct was to hit "X" and select a chapter. Doesn't work. You HAVE to use the touch screen. It's just an inconvenience. The gameplay first starts, and I immediately notice the great graphics. It looks only slightly worse than, I suppose the first uncharted game. It was amazing for a handheld. I didn't see any frame rate issues, and the only bad thing I saw graphically was the fire in the level, it was extremely pixely, but it still was nice and had real-time lighting. Overall the gameplay and controls were identical except for a few controls that required the touch screen, like cutting through cloth and picking up treasure, instead of pressing triangle. I hit the home button to check out the homescreen...and it completely ended the game. I was dissapointed it didn't background the game while simply venturing the home screen of the console.
Well, that is pretty much it, I hope this somewhat helped people out who haven't used one.
Overall it was somewhat of a let down, but I was impressed.
Subject: I've officially used a vita! My impressions! 
