Ebony, be it Gaboon or Macassar, is harder than most commonly available rosewoods. While the tone and feel of the instrument are affected, the most noticeable difference has already been mentioned. Durability. Ebony won't last forever under constant playing, but it does last for a very long time. It also weathers nicely, since the wood is naturally black, and blackens with age.
Timbuck,
The reason ebony finger boards bow after fretting, is because the ebony doesn't give to the pressure of the barbs on the fret wire tangs. Rosewood is soft enough to allow the barbs to push in, but ebony gives very little. Multiply that by 12-20 frets and you end up with a bowed fret board. It's usually not a problem, since you glue it on flat, but here's a trick if it really bothers you. Most fretting saw blades have a kerf of .022-.024". If you're doing it on a table saw, cut each slot twice, moving your fence or means of guide out by a couple thousandths. A nice shortcut is to use a piece of paper as a shim against the fence, then do the cut again without the paper there. Most paper reads about .003", which is perfect. Your fret slots will then be about .027", which is perfect for fretting an ebony board, without severe bowing. Any wider and you may have loose frets, but we work with .028" when doing ebony and it has been working for years. For rosewood and koa, we use the normal slot width.
Or, you could pick up one of those fret barber things from Stewmac. We don't use it for production, but it works great for builds in less volume.