Ashley Parker writing for the New York Times on Twitter hashtags, and how they've begun to permeate the culture at large:
Hashtags, words or phrases preceded by the # symbol, have been popularized on Twitter as a way for users to organize and search messages. So, for instance, people tweeting about Representative Anthony D. Weiner might add the hashtag #Weinergate to their messages, and those curious about the latest developments in the scandal could simply search for #Weinergate. Or Justin Bieber fans might use #Bieber to find fellow Beliebers.
But already, hashtags have transcended the 140-characters-or-less microblogging platform, and have become a new cultural shorthand, finding their way into chat windows, e-mail and face-to-face conversations.
This year on Super Bowl Sunday, Audi broadcast a new commercial featuring a hashtag, #ProgressIs, that flashed on the screen and urged viewers to complete the “Progress Is” prompt on Twitter for the chance to win a prize. Then, in Canada’s English-language federal election debate in April, Jack Layton, the leader of the New Democratic Party, set the Canadian Twitterverse aflame when he attacked Prime Minister Stephen Harper’s crime policies, calling them “a hashtag fail.”
And when Chris Messina, a developer advocate at Google, wanted to introduce two friends over e-mail, he wrote #Introduction in the subject line. No need, he explained, for a long preamble when a quick, to-the-point hashtag would do.