We don't use Gaboon ebony due to stability problems. We have started to use Macassar Ebony for fretless fingerboards. I had to be talked into it, but now I'm sold. The stuff is beautiful of course and it's tone is almost exactly the same as epoxy coated wenge. I will likely wear more than the epoxy but the white line markers show up so much better that I think it's a fair trade off.
Sheldon,
How would you say that Ziricote compares tonally with Macassar Ebony on a Dingwall fingerboard? Bass Player reviewed a Prima Artist 5-string in September of 2005 that had a Ziricote fingerboard and and top - beautiful!
It was ooooh, so nice! Of course, this one helps me get over it! 
