I used brown sugar once to prime a Brown Ale I made. It didn't really make a difference in the taste, but I've been told that what you use to prime the beer won't really lend too much to the overall flavor. Now, I could easily be wrong about that, but personally, I don't recall it making a big difference in the taste. I don't remember how long it took to fully carb as this was before I started taking detailed notes
. But as far as I can remember the beer was at a nice level by 3 weeks. Oh, and according to the Midwest catalogue, you'll need 2/3 cup for a five gallon batch if you're bottling and 1/3 cup if you're kegging.