This column by John Robinson, editor of the News & Record in Greensboro, N.C., offers some examples of good catches. Copy editors there stopped a variety of errors of spelling and fact, including the dreaded "pubic/public" glitch.
The column's headline is "In appreciation of copy editors." The copy editors at the News & Record most certainly appreciate Robinson's kind words.
You can see other mistakes caught by copy editors at Why Editing Matters.