I use a whiteboard. I would love a chalkboard (been looking into the possibility of painting chalk paint on one side of the board). I purchased it ages ago on special. Its a full huge classroom sized one on wheels. I'm trying to find the Crayola Whiteboard markers locally (they have more of a colour range).
I'm not sure how good I would be at chalkboard drawing anyway. I'm more of a cartoonist (I used to do caricatures, so its easier for me when using the vertical board to do stuff in a more cartoony way, anything horizontal I tend to be able to have more leeway in my styles) and I have a feeling DS would eventually run his fingers down the chalkboard *eek.
I know a lot of homeschoolers tend to have more informal waldorf lessons, either the mum has a Main Lesson Book as well (ala ALGF) or they read straight from the text work and show pictures (if available). The chalkboard (for those who have them) are normally for special lessons.
It could be something nice though. Having a nice, gigantic picture for the block in question can add to the atmosphere, plus you can take photos of each drawing you did and add it to the portfolio (yours or the childs) to fondly remember back. Big drawings take a long time though (Rick Tans image for Anatomy (simple muscled man, no background, was what he counted as a "simple" image and it took him about 3 hours. Doing a more elaborate drawing could have you there for half the day or more, which in homeschool terms, is really not ideal.
If teaching multiple children a similar lesson, it would be quite ideal to have something like that (even if you are just writing up a poem to copy or the four parts of a circle), as it allows all the children to see at once (hence why its used in classrooms). Perhaps if wanting a drawing for the week, have a frame in the size paper you use, then just draw on your sketch paper in your free time whereever you are (doctors, bed, during lessons free time etc) then put it in the frame for that week. Its something saveable, gives the same impression, and you aren't tied to the board or time constraints when doing it, it also means if you end up doing that (or a similar lesson again) and you run out of time, you can just pull it out of your folder, and add it into the frame (if doing that, I would suggest keeping it in plastic to stop air-decay etc)
Just my two cents ;)