I used sand on my board.
I just had a tub of PVA glue and worked in sections. I watered the glue down a little, but not heaps, maybe 33% at the most?
Anyway, I'd just "paint" an area with the glue, then sprinkle over the sand, then wait a few hours, tip the board to get rid of the excess sand, then wait a little longer, then "paint" it with glue again.
You just need to make sure the glue is watered down enough not to pool on the surface.
It's super tough once it's done.
As has been mentioned, it's abrasive enough that you don't want to use a nice brush when you drybrush it =)
After leaving it for overnight to dry properly I then spray undercoated black then drybrushed greys (because it's underground) but I don't see why you couldn't drybrush it whatever colour you wanted.
The advantage I see is that I have both the modular gaming hill and the board. The board has sand, the hill doesn't. Miniatures slide around on the hill slopes, but not on the board, the sand gives a good gripping surface.
Anyway, that's what I did and I've been happy with the results!
This page on the blog has the process with pics:
http://simbattleboard.blogspot.com/2010 ... r-two.html
And here's a shot showing the hill and the board so you can see the difference: