Slowly Queries

Hi guys. Can you give me a describe what should i do when get a lot of slowly queries?
Last week i saw such INFO messages in postgres log:

LOG: duration: 8144.361 ms statement: update videos set watched=watched+1, last_view_date='1166057431' where id='106980'
LOG: duration: 7825.637 ms statement: update videos set watched=watched+1, last_view_date='1166057431' where id='99337'
LOG: duration: 7023.592 ms statement: insert into statistics_search(date,search,type,id_member) VALUES ('1166057432','sexy','V','0')
LOG: duration: 6603.307 ms statement: insert into statistics_search(date,search,type,id_member) VALUES ('1166057432','Fun Day','V','0')
LOG: duration: 6093.724 ms statement: insert into statistics_search(date,search,type,id_member) VALUES ('1166057433','party','V','0')
LOG: duration: 5855.535 ms statement: update videos set watched=watched+1, last_view_date='1166057433' where id='102462'
LOG: duration: 5464.827 ms statement: update videos set watched=watched+1, last_view_date='1166057433' where id='103901'
LOG: duration: 8917.981 ms statement: update users_auth set date_last='1166057430' where id='384891'
LOG: duration: 7584.912 ms statement: update videos set watched=watched+1, last_view_date='1166057431' where id='103164'
LOG: duration: 5181.864 ms statement: update videos set watched=watched+1, last_view_date='1166057434' where id='112060'
LOG: duration: 38394.879 ms statement: update upload_synchronizer set lock_status='N' where sess_id='103503'

How i can tune database for quick updates?
I have SATA RAID1.

Thank you all for your answers.

--
Anton P. Linevich