All of the ones within reach of me -- www.ics.uci.edu, www.w3.org,
and a few other less public ones.  Hits received on the server are
important for load reasons (which is why I wrote wwwstat).  Hits
received on the proxy are amusing, but not necessary for anyone
operating a non-marketing-oriented service.
I'm not sure if that qualifies under "most" anymore, but it did
the last time I checked.
>>    2) The last action of a cache does not involve a request to
>>       the origin server, so there is no request on which you
>>       can bundle the last set of information.
>
>This is true.  Perhaps at cache-flush time some sort of bulk reporting 
>mechanism can take place, where every URI at www.organic.com is reported 
>on in one transaction to www.organic.com.  Paul, want to revise the 
>proposal?  Yes, it unfortunately is one of those "batch reporting" 
>mechanisms we'd like to avoid, but if the cache flushing is done often 
>enough it might not be hard, and the justification for asking caches to 
>perform this would be "to be a responsibly cooperative net.entity".
If you are already doing one batch report, why not do all the reports
that way?  The larger the report, the better encryption you get.
>>     timestamp HT domain HT [anonymous-id] HT [referer]
>> 
>> would be just fine, with domain being defined by the proxy.
>
>What's HT? and is the record above on a per-hit basis or aggregate? 
Horizontal Tab (I was speaking BNF-ish), and on a per-hit basis.
 ....Roy T. Fielding  Department of ICS, University of California, Irvine USA
                      Visiting Scholar, MIT/LCS + World-Wide Web Consortium
                      (fielding@w3.org)                (fielding@ics.uci.edu)