How robust is PostgreSQL

Hi all,
We're writing an app in Perl and currently using Oracle as the backend
database (via the perl DBI) but due to the costs when we put this live we're
thinking of useing Postgresql.

However we need to know how crash resistant Posgresql is. Oracle has the
"Archive log mode" which writes a log of everything that's casued the
database to change. This allows you to recoved it properly in the event of a
crash.

Does Postgresql have anything simmilar ? I've read about Postgresql's "fsync
mode". Does this guarantee that the data is written to the disk properly and
that the in the even of a crash (such as power outage etc) the database will
still be correct ?

The other question is Backups. Is there anyway to take diferential backups ?
I.E do a full dump periodically, and then make diferential backups from time
to time (preferably to a differet box)

Thanks.