Because of some problems with the Oracle statistics I did a small research.
I have a custom procedure of gathering stats that i call p_x_stats_table. It will gather stats with and estimation of X% of the records. With X corresponding a percentage witch reflect 100.000 records (or all records of table if amount of records inferiuor then [...]

Do you need to increase the shared_pool_reserved_size. Default Oracle puts it at 5% of the shared_pool_size. General recomedations is to put it at 10% of the shared_pool_size.  A good article can be found at DBASPOT or Metalink 146599.1
select ‘You may need to increase the SHARED_POOL_RESERVED_SIZE’ Description
, ‘Request Failures = ‘||REQUEST_FAILURES Logic
from v$shared_pool_reserved
where REQUEST_FAILURES > 0
and 0 [...]

See here a good white paper about query optimizationin Oracle 10g: click here.

After upgrading to Oracle 10g I had enormous performance problems on ALL_% views. Nothing on metalink, nothing on forums. So it took me a while what the problem was. Here is the solution (although the queries using the all_ system views are still less performant then in Oracle 9i):

exec DBMS_STATS.GATHER_FIXED_OBJECTS_STATS;