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As this doesn't change the contents of the page Google lowers my PR, and I am indexed badly.
I have recently changed it to a form method, which looks horrible and is less accessible.
The thing is, some programming forums I have demonstrated what I have done by adding a link with a querystring variable in my message. This would still work, as form and querysting methods both work.
But G will still see this link, and maybe keep my PR low. This could cause a problem.
I could, if I was malicious, link to all my competitors with an unused variable in the querystring, "www.example.com?lower_pr=yes". Google would find this, but see there is no difference in the HTML and see it as a duplicate page.
Isn't it about time G fixed this problem, as I have talked about it before.