I came across this paper on Twitter
"Two Bitcoins at (sic) the Price of One? Double Spending attacks on Fast Payments in Bitcoin."
http://eprint.iacr.org/2012/248.pdf
Their strategy is to cheaply double spend a coin by using friendly hosts to spread the malicious transaction. They've shown it to work without being detected for approximately 10 seconds, enough time they believe for you to run away from Starbucks with your coffee.
Is this really a problem for fast transactions? I've used fast transactions (Bit-Pay, Coindl and Bitcointorrentz) and they already cautiously wait for around 10 seconds before confirming payment.
