At Econbrowser, James Hamilton takes a crack at evaluating the effectiveness of the Fed's latest quantitative easing tactics (and includes some helpful graphs for anyone trying to teach the subject):

The graph below provides our calculations of the average maturity of publicly-held debt both before and after the Fed's operations, updated to include the first 3 months of QE2. The blue line is the average maturity (in weeks) of debt issued by the U.S. Treasury. The green line is the average maturity of publicly held debt, that is, the green line represents the results of subtracting off the Fed's holdings of Treasury debt. Historically the green line was above the blue. This is because the Fed preferred to buy the shorter-term debt, as a result of which the average maturity of the remaining debt held by the public (green) was bigger than that for the debt as originally issued (blue). However, since the start of 2008, that relation has been reversed-- the Fed has been buying a disproportionate share of the longer-maturity debt, and thus has been a factor in reducing the average maturity.

But also since 2008, the Treasury has been issuing more long-term debt faster than the Fed has been buying it, so that the green line continues to rise over time. What we find in the latest data is that this trend has continued over the last 3 months, even with QE2. The graphs below highlight details of the last year. The top panel is the average maturity of publicly-held Treasury debt inclusive of all Fed operations, that is, it corresponds to the green line in the preceding figure. Although the average maturity in the second and third months of QE2 (December and January) fell a little below that for the first month (November), the average maturity in every one of these three months was bigger than in every month of the two years prior to QE2. The second panel shows the fraction of publicly-held Treasury debt (again, after netting out the Fed's operations) that is of 10 years or longer maturity. This has gone on to make new highs in both December and January.

Our conclusion is that if QE2 made a positive contribution to the improving economic indicators since the program began, it could not have been through the mechanism of shortening the maturity of publicly-held Treasury debt.

There are, to be sure, other places where the Fed's QE policies could have made some sort of impact, and Hamilton notes this in his post.  Read Progress report on QE2 here.