Associated Press editors last week updated employee guidelines to include new rules for social media sites such as Twitter: "When tweeting, remember that's there [sic] a big difference between providing an observation ("I nearly bumped into Chris Matthews outside Penn Station") and an opinion ("I nearly bumped into the loudmouthed and obnoxious Chris Matthews")." So remember, if you work for the AP and want to call Chris Matthews loudmouthed and obnoxious, don't do it on Twitter. Write a set of "guidelines" instead.