First of all, the built quality is great. Yes, it has the same polycarbonate back panel as Note 10.1 and it moves little bit if you press on it in the center (which is not part of the typical tablet use scenario), but it feels really solid and not flimsy. Probably little better than Note 10.1, due to the fact that the back is one piece and wraps around the screen nicely and having less plastic parts merging into each other creates less movement and creaks. The full glass front with the integrated speakers on each side works very well.
The Series 5 hybrid is definitely designed for a landscape use. It's too narrow and awkward if you hold it in portrait mode. The thickness is similar to Note 10.1 and it doesn't feel particularly heavier. It comes with a power block (very similar to what you get with laptops), so while traveling, that will add some extra weight.
The stylus is smaller than the one that comes with Note 10.1. (it's slightly chubbier), and it's white. I played with S-Note for a while and it works very similar to what we have on the Note. Palm rejection may not be as accurate as on the Note 10.1, because after writing few sentences, there were 3-4 small lines under my hand where it was resting on the screen.
As for the performance of the Atom, it feels perfectly fine for browsing, e-mail, etc. I haven't noticed any lag while navigating from screen to screen, but when installing programs, moving to something else took a bit extra. It includes a 64GB SSD, but out of the box it has 34GB free. The screen on the Note 10.1 is more brighter compared to Series 5. I would say the resolution is similar in terms of sharpness, pixellation, etc. Since the labels are a lot more smaller in the desktop mode (see below), you can see the pixels in the letters under icons.
Unfortunately, it doesn't come with a preview of Office 2013 that was going to be upgraded to full version when released (this was mentioned for RT devices, but I remember reading it somewhere for the X-86 tablets, as well). It doesn't include Office 2010 either (you have to buy/install it separately). Since office 2010 is not touch optimized, using the stylus is a must. From this aspect, it feels like it was rushed to meet the Windows 8 launch date. This is a mistake on Microsoft's and Samsung's part, because the X86 machines are marketed as "productivity oriented" models as opposed to the Windows RT models, and the lack of touch-optimized Office suite takes away from it significantly. You can use Office 2010 on it without any problems in terms of functionality, but it's not tablet/touch optimized, and you'll definitely need that stylus.
This is my first encounter with Windows 8, so part of the learning curve is due to Windows 8 itself. Although, it's very easy and enjoyable to use it in the tablet mode, I find myself hitting that "Desktop" tile and using it as a "regular" computer. Over time, I'll probably move away from this habit. Once you are at the Desktop, you become aware of what's running in the background and it's a full Windows on a 11.6" screen. I thought the navigation would be a problem without the stylus, but it works OK, even though things look a bit small. After spending few minutes with it, you immediately realize that you're in Windows territory (pop up windows from Norton, security update reminders, restart reminders after installing the updates, etc.).
As of know, it feels more like a "computer" rather than a "tablet" if that makes any sense. Until I spend about a week with both, I won't form any opinions. I wish Office 2013 was included, since it's one of the most important factors for people considering an X-86 based tablet.
Let me know if you have any questions. Once I have some time, I'll make a more detailed side-by-side comparison of both tablets and add some more pictures.