Here's our internal data on this. Based on page view data (values below are page views) and using the statistics from Google DoubleClick Ad Planner (http://www.google.com/adplanner/static/top1000/) we have the following for the last 30 days:

    Wikipedia.org    6,000,000,000
    Twitter.com      5,900,000,000
    Amazon.com       4,900,000,000
    Aol.com          5,400,000,000
    Zynga.com          460,000,000
    Total           22,660,000,000

Then looking at our own internal network for the last 30 days we see:

    CloudFlare      27,066,719,054								

So we did about 4.4B more page views than the combined sites above which would actually leave us room to add LinkedIn and Flickr to the list.