From Martin Fowler:
And finally a really interesting one about the trade off between stale data and performance: Eventually Consistent.
Finally let the master talk (Martin Fowler on Domain driven Design Community site):
I'm a growing fan of a separate reporting database. This can reduce the load of complex queries on the operational database, provide a denormalized schema that makes it easier to write queries, and acts as an encapsulation of the operational schema. The downside is that it will lag the operational database to some degree, but often people are quite happy with yesterday's data rather than todays and messaging systems can be used to keep in sync within minutes if you need to.It says it all !