Bucardo just released a major version (4). The latest version, 4.0.3, can be found at the Bucardo website. The complete list of changes is available on the new Bucardo wiki.
One of the neat tricks you can do with Bucardo is an in-place upgrade of Postgres. While it still requires application downtime, you can minimize your downtime to a very, very small window by using Bucardo. We’ll work through an example below, but for the impatient, the basic process is this:

Mas:

http://blog.endpoint.com/2009/09/migrating-postgres-with-bucardo-4.html