Not sure what kind of synchronous replication you're looking for, but note that PostgreSQL 9.1's synchronous replication only guarantess durability of replicated data, not query consistency between master and slaves.
In simpler terms, it guarantees that no committed data will be lost when the master crashes, but slave nodes can still return stale data after rows are modified/deleted on the master. Replication lag still exists (though to a lesser degree).
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