Sign up. There's no catch or hidden fees or anything, and it's open to all Xbox LIVE users, meaning the Silver members finally get some love too, instead of being relegated to redheaded step-child status, like so often the case in the past.
The program is very vaguely described as allowing you to "earn Microsoft points for doing things they already do on Xbox LIVE." Obviously we're not going to be getting free points for playing games and watching Netflix all day. Points will be earned by renewing LIVE subscriptions, activating Netflix (for the first time only? Lame), taking monthly surveys, and purchasing select Marketplace content. Select content? I don't like how that sounds.
Regardless, it will be nice to earn 10 and 20 points here and there, when you probably would be spending money on these things even without the rewards program. Now if only we can get some sort of GamerScore rewards program.
via Major Nelson