You have to remember your life can often depend on that thing whirling around in front of you, it is better to be sitting on the ground thinking "damn that cost me a fortune" than to be sitting in the air in total silence thinking "damn I wish I had spent that money"
This is how Lycoming defines a prop strike, and it will suprise a lot of you.
http://www.lycoming.textron.com/supp...dfs/SB533A.pdf
Rotax's is similar see
http://www.rotax-aircraft-engines.co...kus/d04167.pdf
http://www.rotax-aircraft-engines.co...kus/d00288.pdf
The fact that you are asking means if you have had one you have concerns over it. Which brings me back to the top of this post.
An Essex Flyer’s Diary prop strike