One of the primary reasons I would get an Asus S400CA-DH51T or the Lenovo S230U would be to write on the Microsoft OneNote application to take notes during class. However, I've only seen people press with their fingers on the screen.
Do those new screens accurately capture handwriting/drawing with a stylus?
TL;DR: While you can write using a stylus, there are tradeoffs, and it's generally not worth the trouble.
These touchscreen Ultrabooks have capacitive touchscreens, so if you wanted to, you could get an iPad stylus, like this one, and use it on the touchscreen.
However, because they don't have active digitizers, they cannot get the resolution that conventional Tablet PCs have. As a result, you have to write much bigger and more deliberately than you would with, say, pen and paper or a tablet with an active digitizer.
It depends on the ultrabook.
Some might only have the touch screen. And as was mentioned, you can use a capacitive touch stylus to do some writing on the screen, like how people take notes on their iPads. However, this is inferior to using a digitizer stylus, which support pressure sensitive writing, higher sensitivity, better palm rejection, hovering, and support for stylus buttons (for things like eraser mode and right-clicking).
Some ultrabooks and tablets do have digitizer stylus support. I don't have a complete list, but I do have a Sony VAIO Duo 11, a convertible tablet/ultrabook with a digitizer stylus. I believe the Lenovo Twist, Samsung ATIV Smart Pc Pro, HP Elitepad, and Microsoft Surface Pro all have digitizer stylus support.
These devices would work very well with OneNote. In fact, that is what I use mine for at work.
I'm also using the Sony Duo 11 and it's N-Trig stylus works very well with OneNote (I like the Office 2013 version a lot) and also excellent with ArtRage. However, currently no pressure support for Photoshop or Painter12, but that might be fixed Q1 2013 according to N-Trig support. The Surface Pro will likely be wonderful for inking, but battery life? The Sony has the option of the slice battery giving you all-day power. Later in the year, there will be a whole new crop of Haswell low power CPU powered tablets, and I'm sure a few will have pressure sensitive styli... patience will be rewarded!
Certainly, the pen has a better resolution than the finger. However, the real power of the pen is that it does different things than the finger. The pen draws. The finger moves and zooms. When the pen hovers, the finger can't accidentally tap other stuff, so you can rest you palm wherever you want and get some precision into your pen strokes. Drawing with a pen is also much better than the finger, because when you draw with a finger, you can't see where you are drawing. Those silly rubber tipped styluses do not do what a pen does, they only emulate a thin finger.
