Grammar Pedants
http://www.thedailymash.co.uk/news/society/people-who-highlight-minor-grammar-points-are-amazing-2013082378916

Homophones are mist two easily.
Eye don't no weather David Dickinson wood bee aloud too cell rump stake at auction.
Addicted to Proofreading
http://www.grammarly.com/…/4-reasons-you-should-form-a-pro…/ www.shelliemarloweproofreading.co.uk
Mother's Day or Mothers' Day?
http://metro.co.uk/2014/03/30/mothers-day-2014-how-poor-grammar-ruins-special-days-for-us-pedants-4680159/

Typos
http://www.toptenz.net/top-10-typos.php

Odd Errors
This isn't a common error, but it only needs to slip through the net once, for the entire content to be spoiled.

The Auto Correct Brain
http://www.theguardian.com/media/mind-your-language/2013/aug/09/mind-your-language-brain-mistakes

Plural Apostrophes
What puzzles me most is not the use of them, but the inconsistent use of them. How did 'specials' manage to escape unscathed?