A couple weeks ago on Shark Tank Australia there was some lady trying to get funding for her website "Rich Gurl" (http://richgurl.com/) essentially what she does is goes out and scrapes sales from all of the major retailers, then when someone clicks a product and heads to that website a cookie is saved on your machine for a few weeks. Any purchased you might make in that window is counted as an affiliate sale and it is NOT illegal. This is essentially what Bit.ly are doing with their shortened links.
What Bit.ly are doing here is not illegal, it might be a bit deceptive but not illegal. The best course of action here would be for users of Bit.ly to stop using it and perhaps find an alternative. Eventually if enough people leave then Bit.ly might get the hint and stop what they are doing.