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The trick is the server generates a unique Etag for each visitor.

Then the visitor's browser sends the Etag back to the server (in an "If-None-Match" header), and thus it acts as a quasi-cookie.

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That's the picture I get too, but I don't see how clearing the cache doesn't, you know, clear the cache. It would seem to imply that if the Etag is still around, it's not really cleared - maybe the data is gone, but the knowledge that the data existed isn't. And it persists through privacy-mode.

Which means I/we am/are either misunderstanding something, or the people who designed privacy and cache-clearing tools had a massive blind-spot.

There are many other techniques employed. As soon as one of the techniques works, it re-populates the others. (Cache clearing doesn't affect Flash cookies [LSO's]).

Cache clearing doesn't affect Flash cookies [LSO's]

This is coming soon to a Chrome near you: http://blog.chromium.org/2011/04/providing-transparency-and-...

Presumably other browsers will follow.

It's already shipping in some:

http://blog.sidstamm.com/2011/05/clearing-flash-cookies-usin...

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