Well, the advantage of "Who's Who" is that the nominees don't have to pay money if they don't want to -- they just pay extra if they want their picture included with a listing, or if the parents want to buy the book to impress the grandparents. Even though its a meaningless honor, it's a nice ego boost for a kid who hasn't gotten a lot of other kind of recognition. Plus I've heard of one kid actually winning the scholarship they offer (I think its about $1000), and while my son didn't get that, they did send him a credit card offer through MBNA when he turned 18 that was on better terms than most he was receiving at the time & had a higher credit limit. (My son was one of those introverted kids who could use the ego boost at the time).
But I personally wouldn't go for any sort of "honor" that requires paying money. Technically (from a legal standpoint) - it's not a "scam" because they give you what they promise for the "membership" -- which appears basically to be a subscription to their publications and access to their members-only web site. But it definitely is a waste of money.