Concerns about the OID

Folks,
I'm made rather extensive use of PGSQL's universal OID in my database
design.  However, now that I'm building the interface for my first
transaction datbase in PGSQL, I'm concerned about a couple of things:

1. Has anyone experienced any performance problems relating
tables/classes via OID?

2. Can I add an index on OIDs for a particular table?

3. Int4 seems sort of small for a number that has to uniquely identify
every object in the database.  Are there plans to expand the OID to
Int8?

-Josh

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