FUN FACT: (and you probably already know this but many do not): "fsync = off" is postgresql-ese for "please destroy all my data". Don't do it. Ever. The 9.0 docs are finally improving the language here to indicate that you must not set fsync off if you value your job.

Setting "synchronous_commit = off" nets you 99.9% of the performance improvement without the possibility of corrupting your entire database.