$dbh->quote($post_id) . "," .

A side point, if you don't mind: The code uses dynamic SQL. Instead of building the statement on the fly, please use placeholders instead. That is, something like:

my $cmd = "insert into latlong (post_id,some_text,geom) VALUES (?, ?, 
+?);" 
my $query_handle = $dbh->prepare($cmd);
$query_handle->execute($post_id, $some_text, "ST_GeomFromText('POINT($
+LongDEC $LatDEC)', 4326)");
[download]

Using placeholders tends to be safer, more clear, and does not (usually) require special quoting.