Unix domain sockets

I have written a function that will allow connections to the postgresql
database using tcp/ip sockets written in 'C'.  I have one application (still
in load testing phase) that runs fine and I can still access the database
using psql on unix domain sockets for the first couple of days.  All this
application is doing is inserting records to the postgres database and doing
some querys.  However after about 3 days I start to get the error:

psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

My application is still happy, and I can see the postgres process that I am
using is still chugging away.  I have also installed postgres on another
machine and established that psql will connect using tcp/ip to the host and
database I am trying to connect to with unix domain sockets.  When my
application completes and I down postmaster and restart it everything is OK
again.  Problem is I consider downing a database as the next thing to a
hardware fault even if it is controlled.

My next step is to add this host to pg_hba.conf and see if I can connect by
specifing the host as an option to psql.

Can anyone point me to the correct e-mail list or does anyone have any ideas
as to what could cause this?

Thanks, Randy