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Try looking for a supplemental result from a search, and when you mouseover it it looks normal. Then try right clicking on it, and you should see the true URL that the result points to.
What is this for? Are they trying to see which links should be lifted out of supplemental status, depending on how many unique visitors click on them?
Interesting... But why would they only track supplemental results?
Let's limit this thread to the specific topic of the redirects that track clicks on the Supplement results. We've got another active thread where we can discuss current changes in the way the Supplemental Index is working [webmasterworld.com].