This law is intended for the "uninformed" people who eat at fast food restaurants and apparently are totally clueless as to what is fattening. I would argue that people who eat at these restaurants do not care about what is fattening. How many of them ordered that lo-cal burger McDonald's offered? How many people order the veggie sub at Subway?
People eat at fast food restaurants because it is quick, reasonably priced, and tastes good. People who are concerned about their weight don't patronize them, or know which items to order.
This is a stupid law intended to give the trial lawyers another cause to sue, as someone said earlier in the thread.
We had a bunch of high schoolers visit the campus I work at. The basement of the Union has McDonalds, Blimbie, Sbarro, and a Sushi joint. I would estimate 90% ate at McDonalds, 6% at Blimpie, 4% at Sbarro, and 0% at the Sushi joint.