Have you read the news about content flagging? yndy did, quite thoroughly, so I recommend this summary if you're not going to read the post and its follow-up. I just skimmed the posts themselves when they came out, but it looks a lot like the love child of flickr flagging and Google safe search. It looks like Six Apart has learned from its past and actually researched this topic before taking action this time, and has come up with something that's at least not persecution-flavored.
How effective it is, well, who can say. Since it only affects searches and anyone can set their age at anything, it doesn't look all that effective. Then again, I didn't want flagging measures, so I don't much care about that.