After reading the above posts about prop safety, I'd like to add one more item while we're at it...

Wooden prop hubs "take a set" after the prop nut has been tightened down...the wood fibers compress after a while, so the prop nut is basically not providing as much clamping load on the prop washer / prop hub.
You need to check the prop nut from time to time, to re-torque it a bit, and this needs to be a part of your regular maintainence ritual. I've seen props loosen while starting the engine, and just slip on the shaft, which is annoying. I've also seen them go flying off into "who knows where" territory...not safe at all, especially if someone gets in it's way.

All prop hubs will take a set, or compress a little bit, even the much harder plastic or composite props. Wooden props are MUCH more prone to do so...especially the softer woods. Some of the newer Top Flite props seem to be a rather light wood...maybe Beech? (I don't recall exactly right off hand )