[gnaritas]

I would depend on whether adding different units together was an error. 1 dollar + 1 euro should be an error. So raw numbers for pure counting is OK, but raw numbers for counting units of a specific measure are not OK, an abstraction should be introduced. If you just willy nilly add feet and meters you might end up missing your desired orbit and losing a billion dollar satellite.

[cschneid]

I agree, and while the project we were on didn't have strong typing of money, what I described was the database storage of the numbers. We did very few calculations, and the system was explicitly USD, so going deep into "proper" handling of money was just unnecessary.

I really do like using the type system to keep track of units (type system either in the object oriented sense, or the haskell type system). This is similar to Joel's old article about using a naming scheme for dirty vs. sanitized strings for the web. It's all a type system, just his was in a language that didn't support language-level types.