For a currency where everyone can see everyone else's transactions, there seems to be precious little information about who (as a general group, not individual) is dumping bitcoins right now. Early adopters getting out? People who speculated in June/July/August and lost cutting their losses?
The volumes are too low. With all the mining investments made in June and without all the hype from news articles there isn't enough money entering the market to support sales. I believe we are coming back to May prices:
I also believe we are coming to the point were bitcoins are not a novelty item or a get rich quick scheme anymore. So answering the question: the people who still buy bitcoins are those who use it (mainly Silk Road imo). The people selling are mostly miners. The minor price movements are speculators day trading and bots scalping the market. But a lot of people left between June and now.