“It feels like high school,” tweeted @JillVanWyke, who teaches journalism in Des Moines, as tweets from other journalism professors rolled in from Austin. “All the cool kids are at a cool party, and I’m home on a Fri night.”

Even as Twitter says half a million people a day are signing up for the service, some of its most devoted users are warning that the tantalizing window it provides on the lives of friends, colleagues, rivals and celebrities can have a downside. In a blog entry, Caterina Fake, the co-founder of the photo-sharing site Flickr, called the anxiety produced by the technology “fear of missing out,” or FOMO.

“If you didn’t know that party was going on, you’d be home contentedly reading your latest New Yorker,” Ms. Fake wrote. “But since you do, you hungrily watch each new tweet.”

The festival, where Twitter first caught on four years ago, mixes new technology with music, film screenings and forecasts of the future of media.

Ms. Fake, who stayed home, said she noticed tweets from people at one party in Austin who wished they were at another party that friends were tweeting about from across town.