Really? Like MarkT, I'm mostly basing my experiences on food products. For example at http://sverigeonline.se/
we see thing in packages of "300 g", "1,4 l", etc... I wouldn't entirely trust what is written on packages exported to the US, but that's an actual Swedish website, right?
We're getting further and further off-topic here...
Yes, that's swedish site but I never said that these units are used on packages. Markings on packages are standardized for international reasons. That inludes units as well as expiration dates.
Grocery stores and markets in Sweden use the hectogram to specify prices for some groceries. My guess is that it's a leftover from the days when the storeowner used a scale with counterweights to measure the goods. I don't know how common this is in other countries.
Decilitres are used as measures in recipes in Europe. The decilitre is the most frequently used measure at least in the Swedish kitchen.
I've never seen the decagram in Sweden but I've seen it being used in German recipes.
I'm sure these units are used in other ways in other countries but the point is that they are
used in the real world. You just have to look a bit further.
I personally also use the decimetre to loosely specify things like depths of snow. A decimetre is technically 100 millimetres but when you say "a decimetre" it's clear that you're not being that precise. Just because we don't use feet, stones or gallons as measurements doesn't mean we don't do rough estimates. And it's not uncommon to use the closest available unit to keep the numbers down.
None of the mentioned units are used for scientific purposes as far as I know.