A pet peeve: People who write or say “cannot be understated” when they mean “cannot be overstated”. Yes, there are times when such folks actually mean to say what they say, but much more common is when someone says “understated” in this cliched context when they mean “overstated”. The upshot, of course, is that they are saying that something is really, really trivial, when they mean to say precisely the opposite.
Here is an example from a BusinessWeek article assessing Bill Gates’ legacy. I have a hunch that the author did not mean to imply that Microsoft’s and Gates’ impact were minimal:
For better or worse, the role that Microsoft and Bill Gates played in such a vast societal change cannot be understated.
For more of this sort of thing just do a quick Google search. It’s legion. I’m particularly fond of one of the first hits in the search, one where someone says, “The dangers of meth cannot be understated.” Whoa, news to me!