OID Question

Greetings,

Here is a simple question:

Is it ok to put a unique index on the oid for my tables? We are in the process
of moving from Progress Software to PostgreSQL. In the Progress world, you
can always uniquely, and quickly find a record by using their version of oid,
which is recid.  I remember reading somewhere that the oid could be
duplicated across the cluster, but would not be duplicated in a single table.
Maybe I dreamed it. What is the recommendation regarding this and why?

Version:
PostgreSQL 7.4.6 on i686-redhat-linux-gnu, compiled by GCC gcc (GCC) 3.2.3
20030502 (Red Hat Linux 3.2.3-42)

Thanks for your input...
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