Use(functional) concurrency supporting languages basd servers for applications which map to a parallel environment more.
Use straight forward HTTP web servers for req-response style requests.
Use C++ whenever efficiency/logging is required.
Develop/use NOSQL based approaches(Cassandra) for semi-structured/unstructured data that can tolerate relaxed consistency.
Develop your own Storage system (which does not require all the metadata and inode entries generally required by general POSIX systems) for photos to get rid of expensive CDN's.
Scribe - Their own distributed/reliable Logging System.
Do not use too many fine grained services - I have seen this problem in companies where too many fine grained services, then result in a drop order on deployment day (pretty painful).
No service private schemas ( Then how do they make changes to databases in an isolated way).