turning fsync off for WAL

Hey,
I am running a postgresql server on Amazon EC2. My current plan is to mount
an Amazon S3 bucket as a drive using PersistentFS which is a POSIX-compliant
file system.
I will be using this for write-ahead-logging. The issue with S3 is that
though the actual storage is cheap, they charge $1 per 100,000 put requests
- so frequent fsyncs will
cost me a lot.

I've been talking to the makers of persistentFS, and one possible solution
is for the file system to disobey fsyncs. I am trying to find out the
implications of this method in
case of a crash. Will I only lose information since the last fsync? Or will
the earlier data, in general, be corrupted due to some out-of-order writes
(I remember seeing this somewhere)?

Thanks,

Ram