Mark Twain was correct. Simon Dumenco is not. In his recent rant at adage.com, Simon informs us the press release "officially died" this past summer. It's interesting to read the handful of comments. All of them are negative. A quick Google check shows articles as old as four years ago heralding the end of press releases.
That's interesting, because clients still ask for them and, oftentimes, issuing press releases makes sense.
Now, let's be fair to Simon. His recent post talks almost exclusively about "celebrity" America. His logic shows fault with his assertion "As the celebrity-industrial complex goes, so goes the rest of corporate America." While it makes perfect sense for celebrities and their followers to talk in 140-character snippets, doing so when you have something of substance to say is irresponsible.
So, perhaps companies will tweet about earnings and whatnot, but most likely, such tweets will refer followers to a URL where they'll be able to read - wait for it - a press release with the news.
UPDATE - John Mayer has now declared Twitter as "over." Now what will we do to communicate?