Extreme PostgreSQL?

We're getting ready to do system upgrades to our postgresql hosting
cluster. Currently, we're using
8-core servers with 32 GB of RAM in each to host approximately 75 end
user databases per server. I'm wondering
if there are particular performance bottlenecks we should be aware of as
we scale the hardware up? Does
PG handle 64 GB of RAM well? 128 GB? 16 cores? 48 cores? SAS/SATA III
with SSDs? (etc.)

A bit of Googling found this thread indicating potential performance
issues at 28ish cores a couple years back
http://postgresql.1045698.n5.nabble.com/MIT-benchmarks-pgsql-multicore-up-to-48-performance-td3173545.html

Thanks,

Ben