did you read about the view in the reference guide?

then just query it.  for example, to find the segments with the most reads/writes, you might:

ops$tkyte@ORA9I> select owner, object_name, object_type, statistic_name, value
  2    from dba_objects,
  3         (select statistic_name, value, obj#
  4          from (select a.*, max(value) over (partition by statistic_name) mv
  5                    from v$segstat a
  6                   where statistic_name in ( 'logical reads',
  7                                             'physical reads',
  8                                             'physical writes',
  9                                             'physical reads direct',
 10                                             'physical writes direct' )
 11                 )
 12           where value = mv
 13             and mv <> 0) b
 14    where dba_objects.object_id = b.obj#
 15  /

OWNER      OBJECT_NAME                    OBJEC STATISTIC_NAME            VALUE
---------- ------------------------------ ----- -------------------- ----------
BOPPS      SYS_LOB0000039547C00007$$      LOB   physical writes           27026
                                                direct

PEOPLE1    DR$WWC_PEOPLE_PROFILE_IDX$X    INDEX physical writes          150350
PEOPLEA    WWC_PEOPLE_FAST_PEOPLE         TABLE logical reads         386025152
PEOPLE_RAW SYS_LOB0000039609C00009$$      LOB   physical reads          1858082
                                                direct


see

for a blurb about the book -- title will most likely change and its due out in the spring/summer.

 

ops$tkyte%ORA11GR2> create table t enable row movement
  2  as
  3  select *
  4    from all_objects;

Table created.

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> select owner, object_name, value ,
  2         (
  3         select bytes
  4           from user_segments
  5          where segment_name = 'T'
  6             ) alloced
  7    from v$segment_statistics
  8   where statistic_name = 'space used'
  9     and owner = user
 10     and object_name = 'T'
 11  /

OWNER                          OBJECT_NAME                         VALUE    ALLOCED
------------------------------ ------------------------------ ---------- ----------
OPS$TKYTE                      T                                 8511488    9437184

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> delete from t;

72946 rows deleted.

ops$tkyte%ORA11GR2> commit;

Commit complete.

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> select owner, object_name, value ,
  2         (
  3         select bytes
  4           from user_segments
  5          where segment_name = 'T'
  6             ) alloced
  7    from v$segment_statistics
  8   where statistic_name = 'space used'
  9     and owner = user
 10     and object_name = 'T'
 11  /

OWNER                          OBJECT_NAME                         VALUE    ALLOCED
------------------------------ ------------------------------ ---------- ----------
OPS$TKYTE                      T                                 1021337    9437184

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> connect / as sysdba
Connected.
sys%ORA11GR2> startup force;
ORACLE instance started.

Total System Global Area  535662592 bytes
Fixed Size                  1346140 bytes
Variable Size             356517284 bytes
Database Buffers          171966464 bytes
Redo Buffers                5832704 bytes
Database mounted.
Database opened.
sys%ORA11GR2> connect /
Connected.
ops$tkyte%ORA11GR2> set linesize 10000
ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> select owner, object_name, value ,
  2         (
  3         select bytes
  4           from user_segments
  5          where segment_name = 'T'
  6             ) alloced
  7    from v$segment_statistics
  8   where statistic_name = 'space used'
  9     and owner = user
 10     and object_name = 'T'
 11  /

no rows selected

ops$tkyte%ORA11GR2> alter table t shrink space;

Table altered.

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> select owner, object_name, value ,
  2         (
  3         select bytes
  4           from user_segments
  5          where segment_name = 'T'
  6             ) alloced
  7    from v$segment_statistics
  8   where statistic_name = 'space used'
  9     and owner = user
 10     and object_name = 'T'
 11  /

OWNER                          OBJECT_NAME                         VALUE    ALLOCED
------------------------------ ------------------------------ ---------- ----------
OPS$TKYTE                      T                                -1020354      65536