* easier to erase
* easier to clean board and erasers
* chalk is cleaner, cheaper, more expressive, less wasteful (no plastic), and there are generally more colors available
* chalk stays at full "marking capacity" until it runs out. Dry-erase markers make you write at less than full contrast for a long while until you toss them.
* chalk dust is no problem if you have windows you can open a little
* sounds better when you use it. :)
* nicer light-on-dark contrast (IMO)
But whiteboard gets chosen by non-experts b/c it supposedly makes less dust for electronics/projectors. Unfortunate.
Presumably, non-experts in the details of your opinion about whiteboards vs. blackboards?
One thing though, when there's direct light, what's written on the surface casts a shadow on the painted back-side. It looks a bit odd.
Also, the same effect results in a fuzzy picture when the glass board is used as a projector screen.
I'd love to experiment with back-lighting the glass board. If would eliminate the shadow-problem, and look pretty neat, I think.
They probably look a lot cleaner than the white ones after years of usage. If the ink in the marker dries out, it is harder to read than it is to, from a whiteboard. Can't think of others for now.
The physicists and mathematicians I know seem to universally prefer blackboards, while everyone else seems to like whiteboards.
I like whiteboards for any semi-permanent or "data-rich" writing (i.e. multi-color), but probably prefer blackboards for intense computation.