I've just made some statistics about the Poloniex ETH/BTC market starting from the first trade (08/08/15), ending with today's last trade at 5:25PM UTC 
(Click on the image to view it in large!)
Total ETH bought (at market price): 41,036,582.23746390
Total ETH sold (at market price): -49,857,216.90288770
Difference: -8,820,634.66542021 ETH
(Click on the image to view it in large!)
Total ETH bought (at market price): 41,036,582.23746390
Total ETH sold (at market price): -49,857,216.90288770
Difference: -8,820,634.66542021 ETH