We are moving to SSD. It just takes a while. This is the last of our servers to not have SSD. But, nonetheless, it seems obvious that for many use cases, one should be able to say, "I don't care if it's on disk immediately. Just be fast."
The "nice" option is to tune "fsync", "synchronous_commit" and "wal_sync_method" in postgresql.conf
If your overall write load is low enough that you will catch up over reasonable amounts of time, the really dirty method is to set up replication (internally on a single server if you like) and put the master on a ram disk. If your server crashes, just copy the slaves data directory and remove the recovery.conf file, and you'll lose only whatever hadn't been replicated.
But in terms of time investment in solving this, it's likely going to be cheaper to just stick an SSD in there.
