How To Scale RoR

I attended one of Sun's executive briefings yesterday and I saw the ideal way to scale any one of the database-driven web development stacks:

http://www.sun.com/servers/x64/x4500/specs.xml

Now that solid-state disks are becoming more reasonably priced, replacing a bank of spindles with solid-state drives acting as an advanced disk cache, that should solve any database latency problems. As long as shared-nothing is practiced in the application layer, this could solve the scaling issue.