No, it really doesn't happen a lot. If it does, you're doing it wrong.

If you don't have parametric polymorphism, you only have two options to implement new containers: a new implementation for each type or using interface{}. The first leads to a lot of duplicate code, the latter requires you to use introspection to use safely.

So, it does happen a lot, or you are making duplicate code.

Or you just don't need polymorphic containers that often (other than the ones that go already gives you).