set timing on
create table t1 as (select * from dba_objects);
insert into t1 (select * from t1);
.
.
.

insert into t1 (select * from t1);
commit;

Oracle9i Enterprise Edition Release 9.2.0.6.0 - 64bit Production
With the Partitioning option
JServer Release 9.2.0.6.0 - Production

SQL> set timing on
SQL> select count(*) from t1;

  COUNT(*)
----------
   7404020

Elapsed: 00:00:29.09

-- delete 1 million at a time...
SQL> delete t1 where rownum < 1000000;

999999 rows deleted.

Elapsed: 00:00:30.05
SQL> commit;

Commit complete.

Elapsed: 00:00:00.00
.
.
.

Elapsed: 00:00:00.00
SQL> delete t1 where rownum < 1000000;

404027 rows deleted.

Elapsed: 00:00:33.03
SQL> commit;

Commit complete.

Elapsed: 00:00:00.00

-- Query is still very slow - even though it's empty
SQL> select count(*) from t1;

  COUNT(*)
----------
         0

Elapsed: 00:00:23.04

-- But now recover most unused space...
SQL> truncate table t1;

Table truncated.

Elapsed: 00:00:00.05
-- Now it's fast again...
SQL> select count(*) from t1;

  COUNT(*)
----------
         0

Elapsed: 00:00:00.00
SQL>