That's just a bunch of FUD. Tainting coins has not worked once in Bitcoins history.
That depends what you mean by worked. If the reports of a blockage of btc-e transactions are correct (I'm not really sure) then people were inconvenienced by the mere attempt to sort through tainted coins, whether or not that attempt was successful. As long as people believe BTC has taint then maybe that perception itself is a problem? This is not the first and won't be the last time we've heard about the concern.
In any case, I have to agree with iCEBREAKER that LTC is irrelevant and the more interesting question is other coins that are actually different from BTC in meaningful ways.