We are still a loyal customer for some of their services. For example, we still use S3 for off-site backups and Route53 is still our primary DNS provider.

For load balancing we have moved to a Route53 (health checks and round-robin) + a group of nginx+haproxy+lua-based frontend boxes.

Everything else was either built in-house or used open-source components and wasn't really tied to EC2 infrastructure.