I don't think any money from MYBITCOIN has been sold off, but it's sudden disappearance has probably caused many people to lose confidence in other online wallets and services.

Silk Road Anon probably has something to do with it. It hit the news around June 1st (http://www.google.com/trends?q=%22silk+road%22&ctab=0&geo=all&date=ytd&sort=0). Give people 5 days or so to link their bank accounts to Dwolla and they're all buying on June 6th and Bitcoin reaches ~30USD because of the frenzy. The drop in value is the dealers selling back their BTC for USD over the following month.

Once people start to see the price dropping week to week they hold off buying more BTC to see how low the price can get.