Twitter communicates about their recent outages; a great post.

Our direction going forward is to replace our existing system, component-by-component, with parts that are designed from the ground up to meet the requirements that have emerged as Twitter has grown [...] We keep an eye on the public discussions about what our architecture should be [...] Many of the best practices in scalability are inapplicable to the peculiar problem space of social messaging.

I totally agree with them. Scaling, refactoring and migrating a system already in production — without stopping it for a month — is the real challenge.