The way a bubble works is, people get enthusiastic about a thing, so they buy a lot of it, and its price goes up. Then people realize the price is too high, so they sell a lot of it, and the price goes down. All of your favorite market things -- supply and demand, buyers and sellers, the price mechanism -- get a workout. It is a good time, unless you bought the thing near the top.
Today's Wall Street Journal has a terrific story about how mutual funds that bought stakes in large closely held technology companies are now writing down some of those stakes: