peer-to-peer replication with Postgres

I'm considering using a cloud hosting solution for my website. It
will probably be either Amazon, Rackspace or Hosting.com. I'm still
comparing. Either way, my site will consist of multiple virtual
server instances that I can create and destroy as needed. Each
virtual machine instance will be self contained, meaning it'll run the
website and its own instance of postgres. The website will only talk
to the local DB instance. However, if I'm running several machine
instances, I want all the databases to keep in sync preferably with as
little lag as possible.

This is not a master/slave replication issue where there's one big DB
that's always up and everything syncs to, this is basically total
peer-to-peer replication where any time data is updated on one server,
an update command gets sent to all the other servers. I would also
have to address the issue when I provision a new virtual server, I'd
have to import the current data into the DB seamlessly.

What's the best way to do this? Looks like something like pgPool
might be what I want, but I haven't looked into it deeply yet.
Thanks!!

Mike