You'd have to be... er... living on a desert island not to know that the CBS show (about living on a desert island) Survivor is the biggest hit of the summer... And if you like keeping score, head on over to Survivorsucks.com - they're six for six on who gets voted off the island.
Speaking of Survivor, it's slightly less interesting er... on-air sibling, Big Brother premiered this past week. 10 people, locked in an IKEA-in-hell style house, built on a CBS lot here in LA (and not too far from my house), on TV 5 nights a week? I feel sorry for those producers and editors... If 5 nights a week isn't enough, you can catch them on live webcam feeds 24/7... There's even a secret control room cam.
Course, the best "reality" show (if you want to call it that) of the summer has to be TLC's Junkyard Wars.