Does the Platinum Pass from Kings Island work at the Cedar Point gates this year? Because last year I had to go to the guest relations office and sign my name and they gave me a stamp to enter the park.

From the KI website....

PLATINUM PASSES - This pass gets you unlimited access and FREE Season-Long Parking at Kings Island and all other Cedar Fair amusement and waterparks during the 2008 season. Plus, you'll enjoy a long list of VIP benefits like Early Ride Times, Meal Deals, Early Entry to Boomerang Bay and much more.

yes, they work at any of the gates

Yes. I'm a KI platinum passholder, and I've used it to get in to CP 4 times this year.

That pass gets you in to CP at 9 am (1 hour before the general public), so take advantage of that. Get to the gate around 8:30 so you can be one of the first in the park. That's what I always do. I did that last time and pretty much walked right on to Millennium Force. I got a second ride in on MF, and a ride on Maverick, all before 10 am.