I took delivery of my new NC20 just today, so while I can't say what it's like with extended use I already have a good idea - excellent. What a gorgeous little machine! This is an excellent mix of style and substance with great functionality. The build quality is excellent, very clean lines, very solid.
The initial setup process is very simple - simply charge the battery (only takes about an hour), and fire it up. It'll need a couple of reboots while it sorts out its restore partition etc, but once that's done you can crack on with using it.
The keyboard is just about the best laptop keyboard I've yet used. It's very quiet, with a smooth travel so it is great for quick typing. One slight quirk is that the Windows and context menu keys have been swapped over for some reason (even on the UK layout). I'm not sure why, but as others have suggested, these can be remapped.
The screen is fantastic - very clear, though it does need a bit of adjustment to the gamma etc. as its default settings are a little washed out. I also like that the NC20 has only a tiny black border around the edge of the screen so it pretty much goes right up to the bezel - no wasted space.
This is also a very quiet machine, and runs nice and cool. Even the hard disk seeking is essentially inaudible. I updated the BIOS, RAM and display drivers on arrival, but apart from that everything arrives with the latest versions. Networking XP Home to my Pro desktop was easy, although I did have some initial difficulty getting the wireless to work with WPA, but it's fine now.
Some users (on other sites) have bemoaned the single bar that acts as both mouse buttons, but it's really not problematic. It's soft, and flexible enough that both buttons can be pressed at the same time if need be, so it's really not a problem.
One nice thing is the lack of bloatware this laptop comes with. There's software for the webcam, a bunch of Samsung's own utilities where the majority are genuinely useful. There isn't really anything you don't need. The only items I've removed are McAfee Internet Security (it's only a trial version anyway and I have alternatives) and Adobe Reader, which can be ably replaced with Foxit Reader which is much smaller and faster and suited to this type of machine.
All in all, this notebook is a delight to use, stylish and just works brilliantly. If you're after a great laptop, I'd heartily recommend this one. I spent quite a while researching my choice and I have to say I can't imagine having chosen a better machine.