> Is there anything I can do to the Slony configuration (or source) to
> reduce this chattiness?  I could afford as much as a 1 minute delay in
> updates.

You may try to play with -s and -t parameters to slon

hannu at dev2:~$ slon
usage: slon [options] clustername conninfo

Options:
    -d <debuglevel>       verbosity of logging (1..4)
    -s <milliseconds>     SYNC check interval (default 10000)
    -t <milliseconds>     SYNC interval timeout (default 60000)
    -g <num>              maximum SYNC group size (default 6)

Another thing , you may use ssh tunnel with compression

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Hannu