I upgraded to this from a ThinkPad Edge which had been struggling to keep up with my demands, and I honestly think it's one of the best decisions I've ever made. I'm a big ThinkPad fan and really wanted an Utrabook, but the X1 Carbon simply didn't seem to be delivering, especially for the prices they're asking.
The NP900X3C on the other hand is near perfect.
The screen is easily the best I've ever seen on a laptop. Great viewing angles, no glare, fantastic deep blacks and bright whites. I think 1600x900 is perfect for this size screen. It's high enough for me to code in Eclipse without difficulty, something which I really can't do on a lower resolution screen.
The keyboard is good, it's not fantastic, but I have absolutely no issue typing for long periods of time; coding isn't an issue either. There's a little bit of response in the keys, just enough to make it comfortable, however it's not the best typing experience on a laptop ever. One issue I do have with the keybaord is the tab key. It feels just a bit too "clicky". There's something not quite right about it - maybe it's the noise it makes, but it feels slightly different from all the other keys.
The keyboard backlight is really nice. It's not bright, and you'll actually question if it's on or not, however it's just bright enough so that you can see what's written on the keys when it's dark and no more. It's not bright enough to distract, and it does the job well. I think it's a really nice touch.
The touchoad is a bit of an odd one. It's not bad by any stretch, and actually using it to move the cursor and scroll is really nice, however clicking is a tiny bit stiff. I find myself making a lot of mistakes. I'm not sure if it's simply taking some time for me to get used to it, or if the drivers need work, but I sometimes find myself making clicks that I didn't want to make, so much so that I've actually disabled tap to click.
Performance wise it's really nice and fast. The i5 does the job, it's not the fastest CPU on the planet, but the machine is very fast and very responsive. Fans are near silent. I've managed to make them kick in a few times, but only when doing some fairly intensive processing, and even then they're not loud.
Software wise, I removed Windows and installed Ubuntu 12.10, which needed just a few tweaks (keyboard fn buttons need remapped). It runs perfectly, no issues and I easily get 5 or 6 hours out of the battery with Wifi and a reasonable screen brightness (honestly, if you have the screen at full brightness you'll probably blind yourself - it's that bright). If you're thinking about installing Linux, update the BOIS using Windows first, it fixes a lot of issues.
Speakers are surprisingly good on such a small machine. They're not amazing, but they're better than average and I don't have an issue listening to music through them (which says a lot for them).
Design wise, the laptop is beautiful, I really like the colour and the design. I wish they hadn't included the word "New" before the little Series 9 branding though, every time I see it I cringe a little.
Overall, very happy.