People say "Bless you" when you sneeze because when you sneeze, you're heart stops for a milli-second. - Not true:
http://en.wikipedia.org/wiki/Bless_you
A pregnant goldfish is called a twit - utterly untrue, not least because goldfish don't get pregnant! Nor have they ever been called tw@s.
The cigarette lighter was invented before the match. - True; this was on Qi (which isn't an amazingly good proof, but the best I have)
A duck's quack doesn't echo, and no one knows why. - as stated, this is complete bunkum, and obviously so. A quack is merely a soundwave, therefore it can echo.
Twenty-three percent of all photocopier faults worldwide are caused by people sitting on them and photocopying their buttocks. - Don't know about the statistic, but certainly my friend who is a photocopier engineer agrees that December sees the largest number of call outs, caused by people photocopying their bums.