M1 has already peaked on a 1-year rate of change. However, the Fed cannot assume that bankers will not start lending and increase the M1 multiplier. Thus, the uncertainty principle should cause an early end to QE2.
Here is a 4-week average of a 24-week rate-of-change in M1. My analysis going back to 1965 indicates that a rate in excess of .05 is excessive and a return back below .035 brings trouble to the stock market. It should be apparent how responsive M1 is to the monetary base and thus to FOMC operations.