No doubt, most of us have floored by some truly busy-looking, horrendous Powerpoint slide designs:

http://toptrends.nowandnext.com/?p=913

At one place where I worked, there were alot of truly poorly designed slides for clients...just too much info. packed in 1 slideframe. No consideration that it's being shown in a room of 200 people. Not even 20 people could absorb a busy looking slideframe.

Or eye-straining colours for slide backgrounds, fonts.