slippery slope

[Danzig]

ah, the slippery slope argument...

i was just reading about obama's suggested new rules on guns, and some of the commenters said things like 'they'll take your assault weapons, next it'll be handguns and rifles'.
of course in past discussions about gay marriage, we have people talking about how gay marriage will lead to 'bigamy, marrying animals, etc'.

so, i was just wondering-does anyone know of a rule like those above being passed, that did indeed create this slippery slope and lead to more and more restrictions? i'm just curious to see if this line of logic has ever actually produced the supposed end result.