http://groups.drupal.org/node/18177
Servers
4 - Web servers with 8GB Memory each, Apache 2.2.x + PHP 5.2.x
2 - Memcache Servers with 8 GB Memory each. 9 bins per server
2 - Database Servers with 16GB each running MySQL 5.0.x

Performance Tuning
What we've done so far for performance tuning.

Cache Router (http://drupal.org/project/cacherouter) for Memcache
Boost for caching our homepage in all 5 languages
Convert all tables except menu_router and search_* tables to INNODB
CDN patch FROM http://tag1consulting.com/patches/cdn for Akamai
drupal_lookup_path patch from tag1consulting.com
Add indexes to fix problem with i18n module
Add hack to core for providing lock mechanism for updating menu_router