It's easy to catch people's prediction out in hindsight, with the most common ones being things like "I see a worldwide market for about five computers" from Thomas Watson, IBM's CEO in the 1950s, and "640k is enough memory for anyone" from Bill Gates.
Now there's a website dedicated to collecting these predictions called "Wrong Tomorrow".
A couple of nice ones:
"The market will fluctuate daily, but by 2010, the Dow will soar past the 50,000 mark"
Kevin Kelly, Wired Magazine, September 1999
"It is hard for us with, and without being flippant, to even see a
scenario within any kind of realm of reason that would see us losing $1
in any of those transactions."
Joseph Cassano, CEO, AIG, August 2007
Mind you, Microsoft seem to be the ones with the biggest gaffs, from Bill's assetion above and a more recent one about spam being beaten in 2006, to Steve Ballmer's view:
"There's no chance that the iPhone is going to get any significant
market share. No chance."
Steve Ballmer, 30th April 2007, USA Today
"The latest sales figures from research firm NPD Group show Apple's iPhone 3G
gaining market share rapidly. The handset now accounts for 17 per cent of the market."
VNU Net, 7th October 2008