Attached is an image of working with the Cintiq. You still work between the image and the keyboard.
I reviewed a Cintiq for the Canadian Architect Magazine - 18" version. It was here for two weeks. That is the integrated tablet and display. They have a 21" display now around $2500. Finally big enough. Love it.
You can sketch on it using the stylus, overlaid, say, on a (digital) graph paper background to stay square. But it excells at artistic, free drawing, not disciplined design drawing. Retouching photos is great.
The Cintiq is also great with SketchUp because it is really like sitting with a model in your lap. (insert favorite fashion model joke here) The navigation is always in 3D - a very impressive experience.
I work every day with an Intuos 3 - the medium-sized one - easier on the arm than the large one. Mostly - as a mouse pad for a wireless Wacom mouse that is very light because there is no battery in it. It is really hard to make a rectilinear sketch on a wacom tablet - it is best suited to artistic drawing - sweeps and details. Mostly, I use the stylus for Photoshop work.....
OLD GUY'S ADVICE:
Don't try to keep the old ways when using ArchiCAD.
You just bought a facility where you can precisely model and "draw" (experiment) without consequence. I find myself, when feeling out a design, to be placing walls and drawing rectangular room spaces with the wall tool after the building envelope limit is scientifically established. Or even thick slabs later converted to walls and floors. Or translucent zones to establish massing.
Drawing directly in ArchiCAD has the potential to inform your design more quickly than faking it out with a paper sketch or a paper sketch stand-in done with an expensive digital tool.
The Wacom products are premium and can cause wrist strain because of the need to be absolutely accurate every time, unlike a mouse that has forgiving relative movements....
If you insist on pencil sketching, have your office invest in an inexpensive tabloid-sized scanner [Microtek - $1000.] (or a small one - $99) and then you can afford to draw on fine art paper....
http://www.amazon.com/gp/product/B000066TOR/103-1958642-0955829?v=glance&n=172282
After that, you really only have to decide between your two power lizard choices:
Are you a diplodocus or a brachiosaur?
Dwight Atkinson