Sending an incorrect site referrer to a downstream website doesn't solve the identity problem! HTTP headers have existed even before all these applications came into being. One just has to abide by some of those basics.
For example:
Say you're on this page: http://site.com/article?_uid=123 (_uid being the identity leaking query param) and clicked a link that appears to point to: http://google.com/
When a user clicks on that link, the page redirect the user to http://site.com/redirect?target=http%3A%2F%2Fgoogle.com&...
The server will then redirect the browser back to: http://site.com/article
And when the server sees that request with referrer set to /redirect?target=http%3A%2F%2Fgoogle.com, it will then parse out the target url and redirect the browser to http://google.com.
This way, the target url can be given a meaningful referrer url without compromising user's identity.
The technique I described allows Quora to customize the referrer associated with an outbound link.
<link rel="canonical" href="http://www.quora.com/What-are-everyday-apps-that-use-cloud-computing" />