The Dow was up about 200 points before the Fed announcement, and then promptly moved negative. The Fed announced it would hold interest rates (at least to the degree it thinks they can control them) at historic lows through mid-2013. The Fed was hoping this concreteness might reduce some jitters about uncertainty, but here is my take on what Wall Street heard:
"The economy is even crappier than we thought, and crappier than many private economists think. So, we are going to continue to do the same impotent thing we've been doing for the past 3 years in hopes that somehow it will magically improve the next 2."
I post this in then the Dow bounces back up 200 points.... Maybe it's not just the Fed doesn't know what to do.... ;)