From what I've learnt about Oracle BI Enterprise Edition - I wasn't impressed.

It's a good solid start, but nowhere near the maturity/usability level that the other entrprise BI tools play at.

For example, one of the limitations is that it cannot handle many-to-many relationships in data. (Heck, even Microsoft's BI debut effort aka SQL Server Report Models can handle those).

When you add an object to the business model, you have to define a primary key (not necessecarily directly on the backend database object - it can be done within the model).
If refuses to work with data unless it can be represented with 1:1 and 1:n relationships (star schemas).

The user frontend isn't very feature-rich either.

Working with different data sources isn't a problem - advertised features never fail to work with Oracle products.

Not much familiar with Business objects, perhaps someone else here will be able to comment on that.

You can read these pocket guides for a little more information -
Administration
User Interface