I have found that single inheritence can be useful but it is very restrictive. More than once, I have found an inheritance hierarchy that made sense when first

I have found that single inheritence can be useful but it is very restrictive. More than once, I have found an inheritance hierarchy that made sense when first created no longer models the problem well. It becomes hard to change it at that point. Frequently I find I really want to mix in cross cutting concerns across different hierarchies. This isn't really a surprise; most problems do not naturally decompose to only a single view of things. I don't mind abstract base classes containing common functionality, so it's useful there, but mix ins would be better to be honest.