• Spike Lee was, like many Twitter users, angered by the killing of Florida teen Trayvon Martin. Tweeting the home address of shooter George Zimmerman would have been questionable enough. But Lee mistakenly tweeted out the address of a couple who have a son by that name. They had to leave their home after being besieged by reporters and threats. Lee would later apologize and "reach an agreement" with the aggrieved family.

• Greek triple jumper Paraskevi Papachristou was on her way to the Olympics when she tried a little ill-advised Twitter humor. With so many African Olympians in London, "the West Nile mosquitoes will at least eat homemade food!" she wrote. Her tweet was quickly criticized as racially insensitive, and Greece's Olympic Committee barred her from participating in the Games.

• Oprah Winfrey had been gushing for weeks about how much she loved the new Microsoft Surface tablet, culminating in this tweet: "Gotta say love that SURFACE! Have bought 12 already for Christmas gifts." Unfortunately for her, those words were followed by ... "via Twitter for iPad."