^^ Apu is an abbreviation for "accelerated processing units" reffered by AMD for its upcoming fusion cpu parts. Yes an apu combines a cpu and a gpu by some peripheral interconnect and does not use a pci-e bus to communicate internally.
Well they won't replace gpu's but will give a more balanced setup at a price point. The on-die fused gpu can actually assist the cpu and the external pci-e gpu in computational and graphical tasks. More info will come out once they are released.
Amd bulldozer is a cpu and not an apu i.e it does not have an on-die fused gpu. The upcoming "trinity" cores will be an apu having bulldozer based cpu cores and amd 6 or 7 series based gpu's fused together.
