#1 The Timex DataLink comes to mind. "OK, so we get the user to type in his appointments using our software, then we transfer the information to the watch by flashing the screen! Brilliant!" Never tried one, but always struck me as needlessly complicated. Haven't seen one in a long time.
#2 Handheld scanners. Pointless.
#3 Docking Stations. "Use your laptop at the office with a real keyboard and monitor." Great, except desktop computers aren't that expensive, so many opted for a second computer instead.
#4 Anything made by Zoltrix. You get what you pay for.
Craig