Read scalability has been greatly improved in Postgres 9.2. It scales pretty much linearly to 64 concurrent clients. Goes up to 350,000 queries per second!

Write throughput has been improved as well.

Check out Josh Berkus's (one of 7 core team members of the Postgres dev team) presentation on what's new in Postgres 9.2:

http://developer.postgresql.org/~josh/releases/9.2/92_grand_...