searching oid's

I've been contemplating the idea of replacing my current char(32)
identification numbers with oid's. Apart from the significant space
gained, I was hoping there would also be a speed gain or some other
incentives.

First, I tried searching tables by their oid, but explain returned
sequential scans. Second, I tried specifing the oid as the primary key in
a table, but the oid column wasn't found. Finally, I created an index for
oid which worked fine. In the end, I feel I'm back to square one having to
use the same index as with my char(32) id's. It seems my only gain would
be 28 bytes per row and no speed gain, apart perhaps for building the
index which should be a bit slower for a char(32) datatype rather than an
integer.

If there's something I'm missing, I'd appreciate if someone could share
their tips and tricks to using oid's more efficiently.

Thanks,
Marc