1) The feds have finally cracked wallet(s) used by Silk Road, or he managed to give his keys to someone (he had a bail hearing today - it's an odd coincidence);
2) Drug cartels are now accepting BTC for major payments; or
3) Macau-based junket operators, that provide casino credit to Chinese gamblers because they cannot easily move money out of China, have begun accepting it for payment.
Personally, I think it was just one of the exchanges moving some money internally.
If someone gave me a copy of a private key, corresponding to some bitcoins, I wouldn't consider it payment, as they still have the private key as well (meaning they could still spend the bitcoins at any time).
It's more like a "shared account" at that point.
I suppose if you try to extract the secret key and the token destroys it, it's pretty secure. Of course, you just lost all your money. I can't think of a non-destructive test.
Here’s who (probably) did that massive $150,000,000 Bitcoin transaction (washingtonpost.com)
From the article: "Who was responsible for the transaction? I asked Sarah Meiklejohn, a computer scientist at the University of California, San Diego, for her thoughts. She's the author of a recent paper demonstrating that sophisticated analysis can reveal a lot of information about who is responsible for Bitcoin transactions. She has combined a large database of Bitcoin addresses tagged with their likely owners."
Link to the paper is provided.
In other words, the only way you get to have the money is if you never spend it, except in minuscule amounts.
As Silk Road (and hundreds of years of cash-based money transfers) shows, the fact that BTC is hard to trace hardly makes laws unenforceable.
There were also statements in some previous comments that this transfer was made for free. It is true enough that a Bitcoin transfer doesn't inherently incur a processing charge from a merchant payment processor, but as merchants learned back in the Middle Ages when charging interest was formally illegal, the price of a transaction can hide financing and processing costs. We don't know what was agreed with whom by whom to make this transfer happen. The transfer may have occurred at a higher than list price for something that was bought, to make up for the ongoing inconvenience of receiving a payment using the new Bitcoin payment mechanism.
[1] One example, among many: http://www.consumerfinance.gov/remittances-transfer-rule-ame...