Correct usage has become more, not less important with the advent of the computer.

Please also remember the correct usage of "anticipate", which does not mean "to expect".

Police also frequently control the correct usage of the electronic toll.

The correct usage is the subject of some debate.

Most schools offer courses on the correct usage of contraception.

Correct usage would restrict the term to the last breaths before death.

That's the correct usage that I was brought up (or reared, never raised) to say.

In the sentence posted by Matt, the correct usage is "are".

We use their Dictionary of English as the basis for correct usage.

So clearly from about the 1860s up to maybe the 1930s it was considered correct usage to have a hyphen there.