Concurrent COPY commands

Hello,

I am running some queries that use multiple connections to issue COPY
commands which bring data into the same table via different files (FIFOs
to be precise). This is being done on a SMP machine and I am noticing
that none of the postgres worker processes operate in parallel, even
though there is data available to all of them. The performance is nearly
exactly the same as it is for issuing a single COPY command. Is this
normal behavior, even with all of the separate transactions still in
progress? Would I be better off doing multithreaded bulk inserts from my
C program rather than sending the data to FIFOs?

The machine I am using has 16GB of memory and 8 cores, so I've tried to
optimize the configuration accordingly but I am a little lost in some
places.

Thanks in advance for your advice,

Phillip