> Furthermore, I don't know if a single database on a database server > performs less well than multiple database > on the same database server.
In my experience even large DBs perform well when queries are on indexed fields and it is much easier to manage data when it is in one place. However, a small DB should always outperform a big one, so I suppose multiple DBs are quicker than one single one (with the expensive of more memory and management and backups etc). Real scalability always comes from splitting data across several physical servers.
