Here's my theory:
The artificial deflationary pressure that has characterized the last few years is really the result of proactive, intentional FED policy. In other words, this pressure is not the result of fundamental macroeconomic fluctuations, such as an elevated demand for money and/or a contraction in the supply of it, but is almost entirely due to the fact that the FED is paying interest on reserves and therefore constricting velocity. Their intention is to essentially 'trap' the trillions of dollars in high-powered money within the financial sector and banking system in order to (1) recapitalize failed institutions, (2) stabilize expectations, (3) reduce the pressure of growing deficits (ease crowding-out effect) and (4) stimulate the wealth effect without simultaneously elevating interest rates and causing torrential inflation.
Unfortunately for the FED, it must and will fail in this endeavor. Velocity is naturally picking up as the economy recovers and begins the re-structuring process. Once velocity rises, the trillions of dollars in high-powered money that the FED has injected into the financial system will enter circulation and prices will therefore inevitably rise. Inflationary expectations will take hold and investors will flee out of the bond market leading to a major spike in interest rates.
The FED cannot counter-act this process by pursuing a counter-inflationary policy because open-market sales will only put additional pressure on already rising interest rates, and due to collapsing bond prices, it can only succeed in sucking out a mere fraction of the high-powered money that it injected into the system.