What I like to mention here, like I already described before is the dangerous game the Vinklevoss are playing if they decide to "prop up".
If they leave it at the 200K and be done with it it wouldn't have any dire consequences, maybe siphon a few buyers off mtgox but overall stabilize the price.
However if they do prop up it will lead to a very chaotic market where due to insufficient liquidity prices rally up crazy and crash instantly after the liquidity returns.
There is an interesting academic work on the subject which you can observe here:
http://demonstrations.wolfram.com/TheHazardsOfProppingUpBubblesAndChaos/I'm not too concerned about the prop, due to limited supply of coins
In a normal bubble, the asset's supply will increase following the price increase, so when price finally reached a turning point that the amount of fiat money supply is not enough to support the price, the added asset supply enter the market at the same time at its biggest scale, so the price will crash hard and long
But for bitcoin, supply is always the same, when the price rised, the liquidity will immediately become a problem, so price rise quickly and crash quickly, like a storm in summer, shake out speculators, but does not really have big negative effect for long term investors(The rise and crash is so quick that most of the investors just do not feel it
)
And a fast rise in price and crash will attract a whole new group of investors who were watching on the side line. Previous owners might have incentive to sell the coin when they had great profit, but why cash out to USD if bitcoin itself is even better in holding values? So most of their sales will be small scale, or not at all if they could spend coins to buy other things
