PostgreSQL Guide for Oracle Users?

I have been using Oracle for years, but have just
started with PostgreSQL. I've downloaded & installed
the software (v8.0.2), and I'm slowing reading my way
through the manual.

Is there any sort of documentation, or a FAQ, or
tips/tricks, or just anything that shows differences
between Oracle and PostgreSQL? Either from a DBA or
from a programmer point of view?

Is there something somewhere that will help people
familiar with Oracle learn what to do (and also what
not to do) in PostgreSQL? For example, it appears
that a transaction in PostgreSQL must start with the
BEGIN keyword, whereas Oracle implicitly begins a
transaction with the first SQL statement issued when
you log into the database.

Is there anyplace to look for any sort of "PostgreSQL
Guide for the Oracle User"?

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