I drink Yerba Mate every day, and when I heard about yaupon, definitely had to try it.
Unroasted, it's very grassy, but refreshing. The roasted variety I got tasted quite similar to mate. It's really good.
The biggest problem I have is that I can get a kilo of mate for $9, but 2 Oz of yaupon is in the $15-$20 range.