[biff]

The lack of anonymity holds Bitcoin back from being an effective digital equivalent to cash.

I was just thinking about this the other day. If you have one well-meaning blacklist on certain Bitcoins, you could have dozens. Stolen coins, drug coins, "Democrat" coins, coins spent on Sunday. Like anti-spam lists, each Bitcoin user could choose which blacklists to pay attention to when receiving coins, but won't necessarily be privy to all the lists that divvy his seemingly fungible pool of Bitcoin into coins that are more portable and coins that are not.

It's not unworkable to have one list that everybody pays attention to, though even that is contentious. It's the ones that will follow that should really cause concern.