Today I read the article Perbu on the “cookie monster”. http://www.varnish-software.com/blog/cookie-monster
I do not agree with “If the client sends you a cookie Varnish will not issue a cached page but instead fetch a new page from the backend servers”.
This is more complicated. Varnish does not care if the client (the browser) send a cookie or not. But Varnish take care of the backend response. If the backend sends a response with a cookie, the page can’t be put in the Varnish Cache.