Grantham agrees with Markman, below. The Fed now is trying, and succeeding, and has succeeded in the past, to inflate assets (stocks mainly), in order to achieve a wealth effect and make the rich feel better so they go out and spend. G says that just as before, this QE2 inflation of assets will end badly. This video of him, courtesy of Ritholtz, is a great companion to his (G's) October letter referenced here and below under "stimulus".
Grantham envisions the S&P getting to about 1500 under QE2, then crashing by half-ish to 950 or so, similar to what happened in the crashes of 2000 and 2008 - This all in about two years.
He thinks overall the next decade will be muddle-through, with 2% or so growth.