A lot of them are not. This makes it really hard for all of us who are watching what we eat...and for those who are diabetics to watch their sugar content, etc.
Here's an interesting blog on the topic: http://www.walletpop.com/blog/2009/09/22/use-food-labels-to-know-what-youre-eating-theres-a-1-in-4-cha/
Maybe it is costly to invest an effort making labels accurate, but I think much time needs to be invested in making labels accurate and educating people how to read them! You'd be surprised how many people can not read a label correctly, or those labels which are so confusing that you really can't figure out! Seriously, if the US wants to really attack the growing obesity problem, they need to start with something 'as simple' as knowing what we're really eating!
What are your thoughts on this?