Hit two things recently that were pretty non-POLA from my perspective.
I haven't seen these documented anywhere ...

First, it appears that when installing Slony, you _must_ have a node 1.
We were planning to use "serial #" style node IDs that conveyed some
meaning about what the nodes do (actually, node names would be even
better, but that's a wish).  When trying to create a new cluster without
defining a node 1, Slony gives an error that it couldn't find conninfo
for node 1.  It would appear as if a dependency on node 1 is hardcoded
somewhere.

The second thing that surprised me is an odd limit on the size of the node
ID.  As I already mentioned, we were trying to use node IDs that contain
some intelligence (serial # style), so our node IDs were around 20000000.
I didn't expect that to be a problem, since it's certainly small enough
to fit in an int, but slonik gave a rather cryptic error:
<stdin>:974: PGRES_FATAL_ERROR select "_clustername".initializeLocalNode(20000000, 'Local Slave node'); select "_clustername".enableNode_int(20000000);  - ERROR:  bigint out of range
CONTEXT:  SQL statement "SELECT  setval('"_clustername".sl_rowid_seq',  $1 ::int8 * '1000000000000000'::int8)"
PL/pgSQL function "initializelocalnode" line 26 at perform

Which makes it appear as if the node ID is being multiplied by one
quadrillion before attempting to stuff it into a BIGINT.  when I set
the node ID down to single-digits, the error stopped.

-- 
Bill Moran
Collaborative Fusion Inc.