Has this been challenged yet in a court, when someone reading only the right-hand column decides they feel all lawsuity? Is this sort of 'user-friendly interface' covered by existing case law?

IANAL either, and I wouldn't touch this or anything else that hadn't been vetted by a professional. To me, on first glance, this smells like class-action bait. "Your Honor, the defendants deliberately misled the plaintiffs by placing a 'simple' Terms of Service on their website, but then hid their true intentions in small print which claimed the obvious, prominent version wasn't legally binding." Who needs that hassle?