Yes
More specifically, I have seen people propose designs where people reach for is-a in lots of places where they really needed to reach for has-a. You can virtually see the lightbulb go off when you explain the difference and explain why they really need the other.
The biggest contributing cause that I see for this are people who think that inheritance is good because it is OO and therefore they should use inheritance. But inheritance traditionally is an is-a relationship - that isn't the right hammer when you have a has-a relationship to model.
Cheers,
Ben
