Kombucha. I tried it once, it tasted of spoiled fruit and had the consistency of snot. Needless to say it was they last time I ever had it. It is suppose to be good for you though...
I don’t exactly consider Wikipedia to be completely reliable, but it is interesting that their entry for Kombucha has 2 paragraphs on “health claims” and 4 paragraphs on “Adverse effects”.
Try water kefir. It’s extremely easy to make, relatively inexpensive, and has millions of beneficial yeasts and bacteria, like kombucha (especially if you do a double ferment), and it tastes delicious. It’s like soda, not like liquid yogurt (that’s dairy kefir). Dairy kefir is easy to make, too, and is delicious and versatile.