Mostly I'm pleasantly surprised about how interested and supportive people are when they find out we unschool... but the two questions I get most tired of answering are probably
"But what about socialization?" and "So how do you know if he's keeping up?" I know it isn't fair to be impatient because even though I've been asked those questions a hundred times, it's quite possibly the first time that particular person has had a chance to ask it... so if the person is actually interested, I try to give a thoughtful answer.
I just blogged about the latter question, if anyone is interested: http://www.robinstevenson.com/wordpress/category/blog/homeschooling-blog/
And I read it with fascination! Very nicely put together--