What drives me nuts is that the Nutrition Information has metric units but the front of the package may not (e.g. "One Quart (32 oz)" but no liter equivalent printed).

Worse is that many products have bogus information. I'm not talking just about the inexactness of the methods, but in many cases the macronutrient math doesn't add up.

Total calories should be about (protein + carb)x4 + (fat)x9. Too often, it isn't close. I was comparing two versions within a product line yesterday (chili with beans vs without beans), and the calorie count for one mismatched the macronutrient breakdown by almost 10%.

If you think that's bad, I encountered a package of tofu recently which stated "Serving Size: 1/4 package; Servings per Package: 8"! Things like that really make you wonder about the reliability of the rest of the information on the label...