Illustrator has the capability to export to dwg, but you dont really "draw" in illustrator, oddly. You typically use the "pen" tool which is drawing with a series of lines and editable vertices. I don't know the lingo so well, but I use illust quite a bit at home and work and it's really not conducive to conceptual design in most cases, better as a post production tool (labeling, diagramming, etc.)
I mainly use illustrator to create diagrams and lable raster graphics like plans sections and perspectives.
I also use painterX for alot of my drawings, works weel with tablet, but it's a little quirky (tends to just shut down out of the blue and the UI is crackheadish).
I use photoshop for probably 80% of my work for producing raster graphics like this..
I'm using a wacom intuos 3 at home and work. Still I use up ALOT of trace before I hit the wacom. Hope that helps..
-n