I have a friend who helps run the desk that moves insider blocks at UBS. Typically, as I understand it, there are lots of methods to dispose of these blocks. An insider can drip shares into the market over time, they can put the block up for bid to the i-bank as a principal deal where the bank bids a discount to market to move the whole block. The bank then either hedges or perhaps their traders have been getting short in the days prior in anticipation of taking the block down. Additionally, the Venture firms who distribute these shares generally direct all their investors to the same i-bank to move the shares. The investor can either fill their order at that bank or have the shares moved to another broker.
Keep in mind the black out dates for trading for all inside employees. Also, since the founders tend to love Warren Buffet, perhaps they are predisposed to hold on to their shares, and since prospects look good for the company, perhaps employees will hold on as well.
So, in short, who knows? Maybe you'll see downward pressure, but maybe not. How much of an appetite do other institutions have for these shares? In any case I'd wait for a bounce and a failure at resistance to get short, but that's a personal style issue...just my 2 cents. Good luck.