I just discovered database links in Oracle. This is a very cool feature which essentially allows you to (nearly) transparently pull data from one Oracle database to another. Combined with a view, you can have a read only copy of production data, real time, without giving a user access to the production database directly.
Along with the above link, section 29 of the Database Administrator’s Guide, Managing a Distributed Database, is useful. But I think you need an OTN account to view that link.