temp tables and function performance

Hi,
I am trying to move up in the world with my sql and need to do the following...
I have a subscribers table and I need to export to csv (semi-colon
separated) certain fields - that is fine, but I also need to export a
multi-select field from another table as one string (0 to n values
separated by commas) per line. The problem being that to get the
actual string I have to go via 4 other relations... and as I have
200k+ subscribers this takes a while.
My idea (which seems to work, though I haven't tested fully as it
takes too damn long!), was to do the following. I would REALLY
appreciate any pointers as my sql has never been this challenged!

CREATE OR REPLACE FUNCTION mytest()
  RETURNS integer AS
$BODY$DECLARE kindy INTEGER;
BEGIN

create temporary table tmp_interests(
id bigint,
value character varying(100)
)
WITHOUT OIDS
ON COMMIT DROP;

insert into tmp_interests
select distinct si.subid, rbi.value
from restem rbi, cats cc, trm_terms tt, subrest si
where rbi.key = cc.name
    and cc.catid = tt.modcid
    and tt.tid = si.themeid;

create temporary table tmp_subscribers(
email character varying(200),
format character varying(4),
interests  character varying(1000),
)
WITHOUT OIDS
ON COMMIT DROP;

insert into tmp_subscribers
Select email,
 format,
 my_interests(id) as interests
from subscriber;

GET DIAGNOSTICS kindy = ROW_COUNT;

copy tmp_subscribers to '/home/myname/subs.csv' WITH CSV DELIMITER AS
';' NULL AS '';


GET DIAGNOSTICS kindy = ROW_COUNT;

return kindy;

END;$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

...


CREATE OR REPLACE FUNCTION my_interests(bigint)
  RETURNS character varying AS
$BODY$DECLARE
subid ALIAS FOR $1;
interests character varying;
myinterest RECORD;

BEGIN
    interests := '';
    FOR myinterest IN execute 'select value from tmp_interests where id =
' || subid LOOP
        if interests = '' then
            interests := myinterest.value;
        else
            interests := interests || ',' || myinterest.value;
        end if;
    END LOOP;

    RETURN interests;
END$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

...

select mytest();

If there are errors then please just focus on the logic, as I have cut
back on the number of columns (for clarity) and changed a lot of the
real table/names... Am I going about it the right way? Is there a
better way?
Thanks heaps,
Antoine