CPU : GPU :: GPU : FPGA :: FPGA : ASIC

As the market matures, mining will progress towards more and more specialized hardware. This will allow for a greater hashrate given the same price.

CPU is general purpose
GPU is for several specific applications (mostly games)
FPGA is for even fewer applications, great at crypto
ASIC models will be made specifically with Bitcoin in mind

Bitcoin ASICs are controversial because at first one company will have a temporary monopoly on their manufacture. Expect a big boost in hash rate, and more people complaining about that monopoly until more manufacturers enter the market. Since this makes CPU even MORE obsolete, expect fewer botnet miners and more professional miners with lower profits - which in the long run goes to zero.

Really it sucks for miners but is great for users.