kilo, hecto, deca, (unit), deci, centi, milli. Everybody forgets about poor deca. And nobody says "kilogram", we all say "kilo". I guess back during the French revolution people only weighted food, and that's why we have such a small unit of mass?
I've seen cans both say 33cl and 330ml. Same for bottles.
Cooking instructions are just as bad in the metric countries.
Hectares exist in Spain too. I always thought it meant (hm)2, but it turns out that it's actually h(are), where an "area" = 100m2. They are only used to measure tracts of land (farms, forests, etc.).
Metric countries describe TV screen width in terms of inches, for some reason. Rulers usually have one side in cms and the other in inches. And in Spain, we call a square of chocolate an "ounce" ("onza"). Clearly we have to defend ourselves from American influence.
I am sure I am forgetting more cases were the metric system is not used as it should.
EDIT: A megagram (1000 kg) is always called a ton. 100 kg is called a quintal (this is regional, I think).