I began paper studying the PXF/NSE-1 architecture at the very beginning of '99 and FCS the product in the first years of the past decade. That's why I said it was "many years" ago. Then after leaving the project, I lost interest about it and moved on to other things.
However, I remember that technically speaking, the PXF cannot really accelerate CEF, because the PXF does not take routing decisions, and the CEF table is potentially too large to be handled by the PXF. So, all packets are initially handled by the CPU with CEF, then if some cycle-intensive task (of a PXF-supported feature) is required, the packet is passed to PXF, freeing the CPU for the next packet.Also I remember that the NSE-100 had somewhat different architecture and was not using the PXF in the same way.
Anyway, as mentioned before, personally I believed more in the power of true IOS, and apparently Cisco did too, with the passing of time.
I think the ISR G2 cannot replace the 7200 yet or in the foreseeable future. There are too many things (HW and SW) that ISR doesn't support, also customers want continuity. But, for sure il will become history at some point.
