I've found the most critical difference between OO and FP to be state. Objects are stateful from the moment they are created until they are destroyed. FP is remarkable for its general lack of side-effects - i.e. computations do not normally affect shared state.

I believe this distinction is a critical one because an application with a lot of shared state is more difficult to scale than one without. As another poster pointed out, in a shared addressed space such as a desktop app, this isn't a concern. But if you want to scale an application across multiple address spaces, communicating and synchronizing the state of objects between these spaces tends to be difficult.

So, my tendency is:

Small and shared address space? Tend to use OO patterns and implementations.

Big and distributed address space? Tend to use FP patterns and implementations.

Note, I don't consider OO vs. FP a language choice – I consider it a programming paradigm choice.