reduce downtime when upgrading 7.3 -> 7.4

Hi,

We use postgresql for rather large databases. For a typical installation, a
pg_restore takes a couple of hours, at least (the dumpfiles are usually 2-4
gigabytes or so, including BLOBs). The machines are expected to be up 24/7,
so this dump/restore procedure makes upgrading unpopular. Is there any
(safe) way to speed this process up?

The most obvious question is, can we use pg_upgrade from contrib? It seems
not to have been updated since 7.3, and is generally documented as
untested. What kind of problems can we get, can they be tested for in a
testbed in advance?

If pg_upgrade is not a good idea, how can I speed up pg_restore? Best way
to set things like fsync etc in postgresql.conf? Will it make a big
difference?

We use FreeBSD-4.9 and want to upgrade from 7.3.4 -> 7.4.1.

Thanks,
Palle