У меня работает на PostgreSQL 9.0, Какая у вас версия PostgreSQL?
skytf=> create table things (things_id serial primary key, thing text);
NOTICE: CREATE TABLE will create implicit sequence "things_things_id_seq" for serial column "things.things_id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "things_pkey" for table "things"
CREATE TABLE
skytf=> \d things
Table "skytf.things"
Column | Type | Modifiers
-----------+---------+------------------------------------------------------------
things_id | integer | not null default nextval('things_things_id_seq'::regclass)
thing | text |
Indexes:
"things_pkey" PRIMARY KEY, btree (things_id)
skytf=> insert into things (thing) values ('thing nr. 0'),
skytf-> ('thing nr. 1'),
skytf-> ('thing nr. 2'),
skytf-> ('thing nr. 3');
INSERT 0 4
skytf=> select version();
version
-------------------------------------------------------------------------------------------------------------------
PostgreSQL 9.0.1 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48), 64-bit
(1 row)