'NOTIFY' slows down postgres?

Hi,
  I currently have a tcl program that:  (script 1)
    -communicates with the postgres database
    -'listens' to every update
        ( a notify was previously executed on postgres' side)
    -then sends the new updated information to a client.

  I have another tcl script that:    (script2)
    -communicates with the postgres database
    -runs 400 updates on one table
        ( I change a value and then change it back )
    -prints out the elapsed time.

  So anytime script2 updates something, script1 knows about it.


a.)  When I run script2 without script1, without a listen or a notify,
script2 finishes running in 3 seconds.  (ie: script1 has no clue as to
what is going on... and postgres doesn't let anyone know what was updated)

b.)  Adding a 'notify script1' to the above configuration, script2
finishes running in 7 seconds. (!!)

c.)  Adding script1 ( ie: script1 is now running, listens for updates
and postgres notifies script1 about every update but does nothing with
its new knowledge) script2 finishes in 16 seconds.

Note: Everytime i run script2, the results of parts c increase
steadily by about 1 second.  However, the results of parts a and b have
been consistent.

What is it about the notifies and listens that slow my script down?  What
can i do to make these notifies go faster?

Any help would be appreciated.  Thanks in advance,
cheirie
cshum@cats.ucsc.edu