I love mate!! I love the way it's so sustainable to cultivate. Not only does it prevent deforestation because it can be grown in the shade; it also gives a nice kick to farmers' incomes because they can use their land for two things at once, i.e. tree fruit and yerba mate. An all around benevolent crop!
I also like the effect it has on me. While coffee contains a cocktail of caffeine and muscle stimulant (hence the intense jitters you get after, say a pot or two... trust me I know...), yerba mate has a mix of caffeine and muscle relaxants. This gives you a nice alert but mellow feeling. Makes it a great study drug too!
I had never heard of the stuff before I took a trip to Argentina in late '09. Everyone around in Buenos Aires had these weird looking gourds with metal straws and they were passing them around like peace pipes. Then when I was in Iguazu, my friend and I hung out with this shop keep in a random souvenir store on a dirt road. He made us mate in his own gourd and taught us all the associated etiquette. I came back to the US with two kilos of his favorite brand and two gourds. The ritual of drinking mate is half the fun, too!