halooo, it's me again
I found some scripts on dbasupport.com and ...
script:
select parameter, gets, Getmisses , (getmisses/(gets+getmisses))*100 "miss ratio",
(1-(sum(getmisses)/ (sum(gets)+sum(getmisses))))*100 "Hit ratio"
from v$rowcache
where gets+getmisses <> 0
group by parameter, gets, getmisses ;

I have following results:

"dc_files" 2 1 33,3333333333333 66,6666666666667
"dc_free_extents" 4488 295 6,16767719004809 93,8323228099519
"dc_histogram_defs" 173260 3916 2,21023163408137 97,7897683659186
"dc_object_ids" 11658527 2022 0,0173405214454311 99,9826594785546
"dc_objects" 125661 5650 4,30276214483174 95,6972378551683
"dc_profiles" 782 1 0,127713920817369 99,8722860791826
"dc_rollback_segments" 3303 30 0,9000900090009 99,0999099909991
"dc_segments" 537724 2040 0,377942952846059 99,6220570471539
"dc_sequence_grants" 15 8 34,7826086956522 65,2173913043478
"dc_sequences" 1855 45 2,36842105263158 97,6315789473684
"dc_synonyms" 39904 291 0,723970643114815 99,2760293568852
"dc_tablespace_quotas" 63 9 12,5 87,5
"dc_tablespaces" 18143 14 0,0771052486644269 99,9228947513356
"dc_used_extents" 265 265 50 50
"dc_user_grants" 9142 39 0,424790327850997 99,575209672149
"dc_usernames" 48313 50 0,103384818973182 99,8966151810268
"dc_users" 109016 41 0,0375950191184426 99,9624049808816


it is quite good I think ... am I right ?