The Federal Reserve expands the money supply causing an artificial boom in the economy. With the boom many individuals overextend themselves, then the Federal Reserve contracts the money supply causing an artificial bust in the economy. Then the individual that overextended him/herself loses all of their assets to the banks.
According to the Austrian business-cycle, the Federal Reserve is essential to starting the boom-bust cycle. It is only when interest rates are artificially low due to an increase in the monetary base that systematic malinvestment occurs. This leads to a false sense of prosperity, as producers rush to grab the easy cash and build projects that they think consumers will buy in the future, but the problem is that consumers are not actually saving and therefore the entire structure of production and the meaning of interest rates is twisted and the boom ends, followed by the bust.
This is more of a problem with fiat currency in general, but no matter the circumstance, fiat currency will always inflate at a constant rate. A central bank can limit this of course, but this means the money the people save is constantly devalued. Not to mention unemployment must remain above 0% to stop hyperinflation. The system is broken and does not provide for everybody.
The Federal Reserve is doing an important thing by buying bonds. Besides keeping interest rates low, it is the one of the few things that agency can do to directly stimulate the economy. Without the Federal Reserve, the current lackluster economic situation would be much wore off and much more dire.
I think that the Federal Reserve definitely has its share of critics. It also probably has made more than a few mistakes in the past. Despite this, it is simply trying to do the best that it can to help out the United States economy. They have nothing to gain by hurting it.