When i see a mistake/error/typo/wrongness online, i:

• Fire off an angry email or comment
• Privately email or message the poster
• Stay awake until it is fixed
• Blog about it
• Ask a friend to do something about it
• Possibly chuckle, definitely ignore it, and move on
• Resist the temptation to feed the trolls
• It depends on how passionate i am about the subject
• There's nothing wrong on the Internet