The graph above has been shamelessly stolen from the Wilshire Associates webpage which gives daily information about the performance of the Wilshire 5000.
The Wilshire 5000 is probably the broadest share index available to examine to sharemarket. "The Dow Jones Wilshire 5000 is the best measure of the entire U.S. stock market." Unlike the DJIA or the S&P 500, which only list "blue chip" stocks, the Wilshire 5000 is essentially a marker for the entire sharemarket. Each single number represents $1 billion, which means that the current index of 15,244.07 represents approximately $15,244.07 billion dollars.
So, what happened last night when the sharemarket tanked? Well, according to the Wilshire 5000, there was a loss of 314.21 points: $314.21 billion dollars was wiped out of the marketplace. This represented a one-day fall of 2.02%.
As you can see from the graph above, last nights fall wiped out all the gains made in July so far. But if you look at June, you'll see that June's progress was hardly wonderful either. In fact, the highpoint you see in early June (the peak of the "mountain") has hardly progressed much at all.
Unlike the February/March "dropoff" that you can see there, none of the recent drops have been too bad. The difference is that while the Feb/Mar dropoff ended up being a hiccup on the way up, the last two months have seen the sharemarket go nowhere. It has, in fact, reached a plateau.
Being the bear that I am, I would argue that this plateau may result in a longer-term downturn in the US sharemarket. The subprime bloodbath has affected both the value of the US Dollar and the bond market, and is now threatening the sharemarket.