Every day there are around 5,000 bitcoins mined.  Assuming the miners have a fairly small margin and they have to sell bitcoins to pay their electricity bills*, that means that a similar number will have to be sold daily.  For a $10 price to be maintained, that means the bitcoin economy requires $50,000 worth of outside investment every day, or $1.5M per month.  If you think this rate of new investment is unsustainable, then you would expect prices to fall.

It looks like the largest source of outside investment (other than peoples electricity bills - see below) comes through MtGOX.  So if you want to know whether the price is going to go up or down, just ask Mark Karpeles, or his (real-world) bank how many deposits they get.  You'll see a lot of people say things like "yeah I hope the price falls to $x because then I'll buy", but are they really talking about spending > $10,000 per day on bitcoins?  Because this is the kind of throughput you need to make any kind of noticeable difference on market levels.

FWIW, I reckon BTCs fall to well below $5 and will stay there until either

• someone with real money comes along (hedgefund billionaire?) or
• bitcoins start getting used by more than 1% of online retailers or
• the rate of bitcoin mining decreases significantly (2014?)

* if they are pure miners then they would sell their bitcoins to pay electricity. if on the other hand they pay electricity in USD and keep their BTC, then they are some kind of miner/investor hybrid.  But this doesn't really change the analysis above - it still means that the bitcoin economy need $1.5M of outside investment every month (either through bank transfers or electricity bills) to maintain a rate of $10/BTC.