Thanks for the pointer - I hadn't seen that one.
I don't think that thread explored the ramifications or the possibilities though.

Sure - they couldn't just use this blacklist to stop silk road in it's tracks, because they don't know their addresses,
but they could make it risky to do deals with various 'shady' outfits - because your coins could be tainted and thus taxed.

Stolen coins would be the obvious addresses to add to the list.

Also, a seized wallet from one criminal could provide a bunch of other addresses they could apply taint to.
Honeypot systems could also taint your change.