In my experience, I have come across very few problems that cannot be served by a relational database. Sometimes there is massaging involved, mostly when serializing data structures. Of course, that will have to be done with an Object database as well -- I am not aware of any popular disk storage mechanism that does not store information as a stream of bytes. At some point, someone will have to write a layer to serialize data.

I find myself using DBI because it's quick, it's easy, and knowing it, I can work with many database backends with ease.

In the future, I may need to use another approach, depending on the project. I don't really care if Wall Street claims that wearing ties makes me a better programmer, either.

If writing join statements is too painful, perhaps you or someone else will write a tiny bit of syntactic sugar to define a common 'object', using foreign keys or whatever, performing that abstraction for you. I highly recommend abstracting away nasty details of that sort.