That was actually my main objection to modules vs. typeclasses: The burden often seemed to land on the users of libraries. Typeclasses are usually effortless as a user, though there may be a multitude of sins[1] hidden behind them.

EDIT: Don't get me wrong, there are also advantages to being able to explcitly declare two structurally identical modules as different, but in practice I find that newtypes suffice.

[1] FlexibleInstances, UndecidableInstances, etc. :)