While there last year, it became clear just how ubiquitous mate is. Young people, old people, men, women, children ... everyone carries a thermos under one arm, a mate (the traditional gourd from which it is sipped), a bombilla (the metal straw/strainer through which the unbagged tea is sipped) around at all times. We were at the beach on a hot sunny day, and old men and little girls were drinking the steaming tea in the middle of summer.
I tried mate while in Uruguay. Leo's aunt passed me the mate and, after drinking, my face made it clear that I didn't enjoy the bitter drink. The next time the mate was passed my way, Leo took a photo of my response. His cousin Javier (who wasn't at that gathering) later correctly commented that it was obvious that that wasn't the first time I tried it -- my face wasn't sufficiently twisted.
Mate isn't a new concept to me. My mother has bombillas, and large, traditional Paraguayan tereré (containers made from cow's horns) as decorations in her home. Paraguayans, Uruguayans, Argentines, Brazilians, some Bolivians and Chileans, and (oddly enough) Syrians and Lebanese) all drink mate, although the Paraguayans prefer theirs cold, much to the horror of Uruguayans.
The infusion called mate is prepared by steeping dry leaves (and twigs) of yerba mate in hot water, rather than in boiling water like black tea. It is a slightly less potent stimulant than coffee and much gentler on the stomach. Drinking mate with friends from a shared hollow gourd (also called a mate in Spanish, or cabaça or cuia in Portuguese) with a metal straw (a bombilla in Spanish, bomba or canudo in Portuguese) is an extremely common social practice in Argentina, Uruguay, Paraguay, southern Chile, eastern Bolivia and Brazil  and also Syria and Lebanon.I recently saw this ad, by Canarias, one of the biggest name brands in yerba mate, and thought it was excellent. The second one also captures scenes from Montevideo and the ubiquity that is mate. That led me to many other user-generated videos on how to make mate. The last one included below was the best.
The flavor of brewed yerba mate is strongly vegetal, herbal, and grassy, reminiscent of some varieties of green tea. Many consider the flavor to be very agreeable, but it is generally bitter if steeped in boiling water, so it is made using hot but not boiling water. Unlike most teas, it does not become bitter and astringent when steeped for extended periods, and the leaves may be infused several times. Additionally, one can purchase flavored mate in many varieties
In Paraguay, yerba mate is also drunk as a cold beverage. Usually drunk out of a cows horn in the countryside, tereré as it is known in the Guaraní language, is served with cold or iced water. Medicinal herbs, known as "yuyos", are mixed in a mortar and pestle and added to the water for taste or medicinal reasons.