An important factor during times of historical bitcoin scarcity in the markets (BTC on MtGox's book at the peak has been decimated to an unbelievable 30k, and it is still low with barely 130k): Miners still have unbelievable profit margins, and most probably most choose and chose not to sell most of their profits and speculate instead. As the profit margins go down due to difficulty increase and price decrease, they are forced to sell their Bitcoins to cover their running costs, providing the market with a larger share of the 3600 daily Bitcoins. They will also begin to sell their accumulated coins to take profits if sentiment worsens. Now speculators not only have to compete with other speculators, but miners, and a negative feedback loop can emerge. People find themselves having vastly underestimated both the available and the newly added supply.
The time to buy Bitcoins could be when difficulty begins to deflate again. Admittedly, that could happen much further up if another media hype starts, but the chances in my eyes are relatively small.
Further factors making me more bearish in the mid term: Bitcoin exchanges are being eliminated and MtGox is returning to its monopoly status from years ago. Bitcoin still extremely centralized through mining pools (2 people conspiring can do a 51% attack, and actually have done so during the coin fork), block size limit hindering growth (see SatoshiDice), altcoin popularity rising (LTC soon to be added to MtGox; Ripple emerging as possible alternative). Oh, and of course that there are no popular actually used (ie, by lots of people with lots of volume) economic applications I know of besides SatoshiDice and Silk Road. There is still no Bitcoin economy.
PS: Talking on a scale of weeks/months here, of course. Short term I guess I am mildly bullish.