[pashamur]

That's not exactly true; market value does not exist in a vacuum, it's the discounted future cash flows of the component companies. You can certainly look at the earnings of the component companies, and see how much growth is being priced in with the current valuations (and whether you think that is reasonable or not over the long term).

Now generally timing the market is not recommended; however, if the market has been going up for 5% a year for the previous 10 years versus going up for 20% a year (assuming same levels of inflation), it paints a very different picture, so at least in broad strokes you should be able to estimate where we are in a market cycle (telling the difference between 1998 and 2000 might be hard, but telling the difference between 1998 and 1994 should be fairly straightforward)

http://people.stern.nyu.edu/adamodar/pdfiles/invphiloh/valua...