Evolution of eBay platform architecture

Thanks to Michael Platt's blog. I downloaded the slides of eBay architecture and just finished reading it. The interesting points to me are as follows.

1. Scalability and maintainability are so important for large-scale distributed systems. The scalability problem is the major reason for the evolution of eBay's platform. And maintainability is the major consideration for the future development.
2. Scaling-out is the proper long-term solution for increasing load.
3. The principle of separation of concerns benefits scalability besides easiness of development and maintenance.
4. Combination of synchronous and asynchronous interactions is a good practice.