California already requires that some restaurants, notably fast food chains, post calorie information. In theory this is a good thing. In practice — well, it doesn't work as well as I'd like.
One problem is, the calorie counts are damned near impossible to read if your vision isn't very good. I'll admit, that may just be me. As the population ages, though, more of you are going to find your vision coming closer to mine. (Sorry about that.) The point is, if you can't read it, you probably won't pay attention to it.
The bigger issue is, the calorie counts may not matter to the majority of customers even if the information is legible. I pay close attention to the nutritional information in processed foods at the market. When I'm at a restaurant, though, I'm hungry and I don't much care about calories. My main defense against nutritional suicide is that I long ago weaned myself off fast food chains. I was lucky I had the option. If I didn't live in an area with a decent selection of non-chain restaurants serving not-too-unhealthful food, my hunger and my laziness would have doomed me to drive-thru dining.
Am I arguing against the new FDA rules? No. They might help, and I don't think they can hurt. However, don't get your hopes too high that they'll have a dramatic effect on the obesity epidemic.