Well the FAA is different to the JAA or CAA.
You can log under the FARs whatever they say you can, but don't expect the CAA to recognise those hours.
The FARs also allow one to log "performing the duties of PIC" as PIC. In this case, for example a ME commercial rating, where you NEED 10 hrs of ME PIC (I think, something like that anyway) and the FAA realise that no school in their right mind will let someone "solo" a ME without a rating, or rent a ME having just gained the rating. So they allow someone who performs ALL of the duties of PIC to log PIC despite not having a rating and despite having a FI sat alongside them.