Tolven Inc an Open Source Healthcare Solutions provider recently carried out a benchmark using PostgreSQL on Solaris 10 using ZFS on Sun Fire X4600. The Benchmark report is now available on their website.
The size of the single database instance using PostgreSQL 8.2.6 (32-bit) peaked at 474GB with the largest table having more than 500 million rows. More information is in the report.
Tolven's setup guide for developers which includes information about PostgreSQL setup is also available on their website.