I had it in Argentina when I visited in 1989. It's horrible. It ranks up there with other foreign foods that I was brave enough to try but still remain horrible - like vegimite and fried driver ants.
We visited a Gaucho cattle ranch, watched horsemanship displays and ate that wonderful Argentine beef. After lunch, tourists were invited to join the Gauchos in a drink of Mate at the bar. I ambled on up and took a seat. I should have known something was up when I noticed it was just me and the Gauchos.
Mate is like a tea, and you drink it through a metal straw that has a strainer on one end. It is brewed by loading a gourd up with the leaves and adding boiling water. You leave the strainer in the leaves and suck the tea through the straw.
It is really bitter and rather awful and I'm sure those who drink it regularly claim it is good for you in all sorts of ways. The Gauchos thought I would turn green or throw up and were laughing at me but I finished it, and afterwards they shook my hand :-). THEN they showed me how they sweeten it with juice or fruit or sugar. It was a fun cross cultural moment. It still was awful. I had to gargle with Orangina soda all the way back to the hotel to get some of the taste out of my mouth
Did I mention it was horrible?
This will take you to a short story which tells about the legend of "yerba mate."