I don't know if it's too late, but since there is no other answer yet, I'll chip in the following. On a project where we needed multi-master replication of PostgreSQL databases, we had success with bucardo. The project was not related to OpenERP, but since it is database replication you are looking for, you might as well give it a shot.
It was quite some time ago, and I'm fairly old and no longer remember things very well, but IIRC bucardo was a bit of a pain to set up, but once it was it worked well, at least for what we needed it for.
There are a few other replication systems for pgsql as well, some of which support multi-master replication. But I don't have any experience with them. You'd have to test them until you find one that suits you.
In an OpenERP context I believe that you may also have to take a few other things into consideration, depending on how you are storing your attachements, for instance. But if they are on the file system, then I guess a tool like rsync might be helpful. But I'm not sure if OpenERP 7 still stores any objects on the file system. Maybe somebody who knows more can shed light on that issue?
Please help with this. It must be one of the most crucial questions for a multi-site openerp installation. You cannot compare openERP to the likes of SAP if there isnt a solid way to do this. I'm looking at http://www.enterprisedb.com/products-services-training/products-overview/xdb-replication-server-multi-master - looks like a potentially good option if it works as advertised. Anyone got a better way to do this??
This is a must have feature for geographical distributed installations with poor internet connectivity. Any updates?