To give you an example of the sort of stuff we do behind the scenes at Yammer, here's what my team has shipped:

* a realtime message delivery service which handles hundreds of thousands of concurrent clients

* an activity stream data store serving just shy of a billion requests a day

* a distributed database serving well over a billion requests a day over tens of terabytes of data with ~10ms response times at the 99th percentile

* a realtime search indexing pipeline, complete with a denormalized entity store, index replication and an autocompletion service

* a data export service which basically performs a diff of the state of millions of business objects and sends it out as a streaming ZIP file

* a user account synchronization service which handles streaming JSON dumps of companies' LDAP/AD server data

* an affinity prediction service which provides ranking of arbitrary objects based on past interactions (e.g., who you're most likely to CC on a message)

* an OAuth2 token service for 4MM users

* a collection service for the user events pipeline of our analytics system, handling hundreds of thousands of user events a second

* plus a grip of open-source libraries

And this is a team of seven people (now). The other teams at Yammer ship just as much as we do.