From the FOMC minutes:
"Members noted the possibility that some negative side effects might result from the maintenance of very low short-term interest rates for an extended period, including the possibility that such a policy stance could lead to excessive risk-taking in financial markets or an unanchoring of inflation expectations. While members currently saw the likelihood of such effects as relatively low, they would remain alert to these risks."
Hmmm.. deja vu. The risk is "relatively low?" Really? Look at the markets boys! ALL asset classes!