For example, on one mailing list I'm on, there was a serious discussion started by The Guardian's joke about going to an all Twitter electronic format. While I don't know if anyone in the discussion was actually taken in, the combination of traditional newspapers going to all electronic formats (q.v. The Seattle Post-Intelligencer) and people preferring "newsbites" to real news, this story seemed plausible enough to discuss. kevin_standlee points out here that someone's joke about Bay Area transportation improvements had some better suggestions than some of what is actually being discussed.
However, there is a danger hoaxes that sound good, and this danger is higher on the other 364.25 days of the year. That danger is that people will fall for the hoax and be upset when they learn that it was a hoax, and not just because they were hoaxed.
Several years ago, the list of programs for Capricon was published with the "Lake Wobegon" room track -- originally the "Phineas Taylor B" room track, or so I've been told. One of the panels listed there, but without a room yet, was a discussion on Cordwainer Smith and his work that sounded very interesting. Both robot_grrl and I were considering going to it until we got the program with rooms and found that it was in Lake Wobegon, which disappointed both of us.