I'll admit it – 99% cocoa dark chocolate is pretty gross. Not just the taste, but the texture as well. It's very similar to what I imagine eating mud would be like.
Between 70 and 80% seems to be the sweet spot for getting a good clean chocolate fix without "eww" ever crossing my mind. I really like the Lindt 85%, but there are times when even that seems a bit more than my tongue wants to deal with.
Also, don't try to wash the taste of almost 100% cocoa out of your mouth using Mt Dew. Not that I just found out that that's about as horrible a taste combination as you can get or anything.. no.