A tablet or a UMPC is an entirely different beast. They usually do a whole lot more than just viewing documents, but come with the downside of being heavier. 2-3lbs is brick territory and 3-4lbs is getting into lump territory - not exactly your friend for bedroom or even armchair reading. These devices can also get hot, and it matters how well the cooling vents are designed and where they're placed.
I've used the
Samsung Q1 UMPC which is really light and has a 6 inch widescreen. It did well for note taking, but the smallness of the screen got in the way. Reading technical documents was a real pain and you end up having to scroll around like crazy before you get an idea about whats on the page.
A 12 inch screen might be great for note taking and reading technical manuals, but I think its a bit too big and you're paying the price in weight. Look around for a 10 inch odd screen - I think that'll suit your purposes and also be lighter.
Since you're going to be taking notes, the eink refresh rate will get in the way (slightly, I actually don't mind it).
The whole LCD vs eink display quality depends on your personal preference. I actually used the LCD screen on my UMPC to read countless technical documents without trouble (especially in low-light scenarios), but I can see the eink screen being far more appropriate for curling up in bed for a long reading session.