[spacemanmatt]

> your product supports multiple databases

In this case, I tend to see pretty light loads. You can do this with fairly vanilla (ORM-generated) SQL and design. When your business begins to lean heavily on the database for operations (I saw this in finance) around the clock, and you have to start being more judicious about your queries, these applications are usually the first to buckle.

> you want to use something like sqlite in memory for tests

Only if I have to support sqlite in the field!