simple auto-updating timestamp ?

Hello list,

I suspect, this is a common issue for newbies.
Is there a simple way to have an auto-updating timestamp like mysql has ?

create table something (
   id                int4,
   sometext     text,
   update_ts    timestamp(0),
   primary key (id)
);

Everytime this table gets updated the timestamp should be automatically
refreshed to NOW() ?
I hope someone could point me to an example.