Hacker News Reader

Sure, I clear the cookies every time close the browser. But can't they just store everything as a session on the server?

Yes but they can't correlate sessions with any reliability because of dynamic IPs and such.

I wouldn't say without any reliability. I know that my "dynamic" IP stays the same for months at a time, if I don't interfere.

And, of course, are you aware of flash cookies?

Also called Persistent Identification Elements. Bad mojo, those.

If you're browsing with Firefox, you can take control of flash cookies by installing the "Better Privacy" Add-on.