The biggest issue is replication of the database ... you should check with the PG group to see what the current status is. Without replication you're reduced to restoring from your most recent backup if you have a failure which causes your RAID disk data to go bad (you are, of course, running RAID, preferably RAID 1 not 5, aren't you?)
On the other hand you may want to think hard about whether the odds of losing data on both sides of a disk mirror is high enough to justify keeping an extra server around for database replication (not to mention the fact that this technology is still immature in the PG world). The chance of losing both sides of a disk mirror is really very low and if you have hot-swap drives recovering from the loss of one is automatic once you replace the bad drive and shouldn't involve any downtime.
