I was just reading Nurtured by Love this morning and enjoyed her post, Watching for Gaps. As she points out, we can't teach our kids everything, or make sure they have learned everything, before they leave home to go into the big wide world. It's impossible. We might think they are well-prepared and then they hit an unforeseen challenge.
Whether children have attended school or been homeschooled or unschooled or whatever, they are going to know a lot about some things, a little about others, and nothing about others.
I suppose the only thing we can do is encourage common sense and creativity and optimism, and they'll take it from there!
Of course, if disapproving grandparents see the gaps, they will lay the blame firmly on the fact that you decided to homeschool, even though it's patently clear that their own knowledge is lacking in some areas too, and THEY went to school!