Well, my kids aren't of official age yet, so it's not relevent to me but I've tried to pay attention, and it seems to me that it's not so difficult here at all-
You file a simple form once a year (don't give them more information than they're legally entitled to- I think the links someone gave above explain about that), and you need to test or get an evaluation once a year, with the results going only to you, and you can give the test. The Family Learning Organization, http://www.familylearning.org
can help with both testing and evaluations and are, I'm told, unschooler compatible. You "have to" cover a certain set of subjects, but there's no checking up on you. I guess you also need to be "qualified" to homeschool, by having taken a year or so of college classes or taking a qualification course- the courses seem readily available and not arduous (and maybe even useful), and are not government run, so far as I can tell.
I dunno. When I came here two years ago it all seemed less scary and more legally accepted to homeschool in Washington than in California, where I'd been- California has since seemed to calm down, but at the time it seemed like there were moves afoot to trample independent homeschoolers.