The usual symptom of a spun hub, is typically that the motor will feel like it jumps into neutral every once in a while, or that it cavitates and the RPM's jump. Or if it's really bad, you might not be able to develop much power at all.
As a tip, what you could try doing to diagnose the problem, is marking the hub and the prop. Then run the engine and then see if the marks have moved.
I've heard of that - my motors are winterized now, and I'm going to have both props, and hubs done. I was just wondering if there was a beast called the PARTIALLY spun hub - if that could be the culprit of a periodic vibration at put put speed?