I'll go for *potentially* game changing.
I dream of a hardware miner/wallet that you'd use as your home ATM...plug and play, secure.
That's a pretty cool idea. However, that assumes that what is being kept secure, is still valuable. With this manipulation and no safeguards in place any big money player can destroy Bitcoin. I didn't realize that before, but now it is blatantly clear. Let's use any government that has $1 billion to spare.
They could build massive mining rigs and with the rest, purchase BTC slowly. It wouldn't take long before they would control enough BTC to just continually smash the markets with wave after wave of coordinated "dump attacks". All confidence would be would be lost. Current investors would flee into other currencies and investments. Potential investors would stay away from a corrupt and manipulated currency. It's actually a better Achilles heel than any regulation could dream of having.
So in the end, Bitcoin's greatest weakness, is it's very own principles of non-regulation. The irony is quite amusing.
Worst. Attack. Idea. Ever.
The attacker would be dumping free money until he/she runs out and then the system would continue to run as usual.
Indeed they are free to donate their money to the market. Then again, it isn't really their money to begin with is it?
BTC is so tiny that the FED could just buy enough BTC to make it skyrocket in en epic pump, then crash it to single digits, creating a few notable fortunes and ruining millions of people on the way. Burning people with BTC seems indeed more effective than simply banning it.
Still, they would be burning piles of money, this is an expensive stunt to perform, "affordable" only by an economic super-power willing to virtually destroy money to try to get rid of Bitcoin. BTC is still too small to deserve such kind of attention, if they decide to play the pump&dump game they really need to go till the end, waking up the sleeping monster
In a few years, not even the FED may afford such kind of attack. And if they do, it will be a hell of a ride and nice fight. Keep'em coming.
Someone dumped what, $6 million and left the markets looking like Hurricane Katrina just hit. People are still on the sidelines waiting for the next dump. $6m is nothing as it relates to governments. Bitcoin, IMO, is not ready for a massive attack, with some serious $100+ million. Not saying I have the battle plan perfectly mapped out, but just these Sunday dumps is enough to highlight that the potential is real. This is absolutely an exploitable weakness. Maybe Bitcoin could survive, maybe it wouldn't. As was said, it would be entertaining as hell. 
