Concierge.com's insider take:
Kava is a drink made from the yaqona root, an uncontrolled substance that is widely consumed–and in some cases abused–by Fijians. But the drink is central to Fijian culture, and the social ceremony can be a highlight for visitors. Locals play music and sing folk songs, while one person prepares the kava in a large bowl called a Tanoa. Drinkers sit in a circle and drink their kava one bowl at a time. It's not unusual to drink two or three bowls in a half hour, and maybe up to a dozen over a two-hour period, but it's considered good form to stop drinking before 9 pm so that you have ample recovery time before the following day. Anything more would be considered sloppy and is only acceptable behavior on special occasions and holidays.
Even after one cup, you can feel the drink's effects: your mouth is coated with a thin film, and you'll experience a mild tingling in the back of the throat and tip of the tongue. Kava makes you have very vivid dreams, which could be good or bad depending on your state of mind, and is rumored to help with hypertension and high blood pressure. Kava is also used as a cure for insomnia, though if you drink too much of it, it can have the reverse effect. The hardest thing to describe about kava is how it tastes. It looks like dirty dishwater and people say that's what it tastes like. Let's just go with the diplomatic response–it's an "earthy" kind of flavor that's most certainly an acquired taste.